I understand your concerns (I truly have the same concerns) but, unfortunately, I have no more insight into the future of AIR than you do and, at this moment in time, I genuinely have no news on the future of JuiceboxBuilder.
All I know is that Juicebox itself is still alive and that work has started on the next version (which will likely be a bugfix release).
I really do not know any more than that. I'm sure that the developers are aware of the AIR issues and all we can do, myself included, is hope that JuiceboxBuilder can live on in some form or other beyond the Harman procurement of AIR.
I wish I had more information (good or bad) to give you but I'm as much in the dark as you are just now.

It should be noted that there are alternative ways of creating Juicebox galleries that do not rely on JuiceboxBuilder and AIR. I realise that these methods may not be suitable for all users (and it is certainly a less than ideal scenario) but the Lightroom plugin at least provides Lightroom users with a longer-term solution (with the Pro version of the plugin featuring full control over all Pro configuration options just like JuiceboxBuilder-Pro).

I'm sorry that I do not have any more information at this time but I'll be sure to post back here if I hear anything relevant to this matter.
Thank you for your concern and continued support of Juicebox.

If you were using Juicebox-Lite, then it could have been due to a WP-Juicebox upgrade.
WP-Juicebox comes bundled with Juicebox-Lite and if you upgrade WP-Juicebox, your Pro 'jbcore' folder will be overwritten with the Lite version.
Reinstating your Pro files is a simple task of uploading your Pro 'jbcore' folder (from your Juicebox-Pro zip file) to your 'wp-juicebox' directory (which should take less than a minute of your time). (You could also just remove the Lite 'jbcore' folder from the WP-Juicebox package before upgrading to prevent your Pro 'jbcore' folder from being overwritten.)

The screenshot of your gallery does seem to conform to the screenshot of your gallery settings window. (The screenshot of your gallery windows shows maxThumbRows="1" and maxThumbColumns="6" and this is displayed in the screenshot of your gallery.)

Setting maxThumbRows="6" and maxThumbColumns="1" will definitely make a difference.

If it does not seem to make a difference for yourself, then the problem is almost certainly a caching issue.
After making changes on an 'Edit Gallery' page, make sure that you click the 'Save' button at the bottom of the page and if you do not see the changes you expect to see, make sure that you are 100% certain that you have completely cleared your browser's cache before reloading your gallery's web page. (Sometimes refreshing the page with F5 or even Ctrl+F5 is not enough.)

I've just double-checked all this by creating a sample gallery in WP-Juicebox v1.5.1.2 (using Juicebox-Pro v1.5.1) using maxThumbRows="6", maxThumbColumns="1" and thumbsPosition="LEFT". The gallery displayed as expected. I then edited the gallery (on the 'Manage Galleries' page and swapped the '1' and the '6'. Again, the gallery displayed as expected (with the rows and columns swapped).

If clearing your browser's cache does not help, then maybe the issue is with server-side caching. Your web host could perhaps have server-side caching enabled on your hosting account and, even though files have changed, your web server could still be serving older versions of these files for a certain period of time.
Please check in with your web host and ask if they have server-side caching enabled on your hosting account and, if so, ask if they would be willing to remove it.
Caching can certainly be useful but it can also sometimes be a hindrance to development.

If you click on the attachment link, the image will be displayed. Below the image, you'll see a download link. Each time the image is downloaded via this link, the download counter is incremented by one. (Most people will be content with viewing the image in place and will not download it.)

WP-Juicebox has individual interface controls for Lite options only.
Pro options must be entered in the 'Pro Options' text area of the gallery settings window, one per line, such as:

expandInNewPage="TRUE"
showImageOverlay="ALWAYS"

This has always been the case with WP-Juicebox (and setting Pro Options in a WP-Juicebox gallery is noted in the WP-Juicebox support page here).

You will find the 'Pro Options' text area in the gallery settings window when you first create a gallery.
You can access the gallery settings window for a pre-existing gallery by going to 'WP-Juicebox -> Manage Galleries' (from the WordPress Dashboard side menu) and clicking 'Edit' next to the gallery that you'd like to modify.

Try adding something like the following to a gallery's 'Pro Options' text area, changing the values as necessary:

thumbWidth="75"
thumbHeight="75"
thumbsPosition="LEFT"
maxThumbRows="10"
maxThumbColumbs="3"

The text in the top-left is the gallery title. To remove the gallery title, set  the following in the gallery's 'Pro Options' text area:

galleryTitlePosition="NONE"

The text near the bottom of the image is the caption area.
By default, WP-Juicebox uses the image filename (without the extension) as the image title. ("b-forgiving-1" in your screenshot.)
You can remove this by deselecting the 'Display Image Titles' checkbox (just above the 'Pro Options' text area).
You can remove the image number ("6/6" in your screenshot) by setting the following in the 'Pro Options' text area:

showImageNumber="FALSE"

You can remove the entire caption area (without needing to remove the image title and image number separately) by setting the following in the 'Pro Options' text area:

captionPosition="NONE"

For reference, a list of all Pro Options can be found here.

I hope this helps.

The 'Home' icon is the Back Button, displayed when backButtonPosition is set to either TOP or OVERLAY (and backButtonUseIcon is set to TRUE).

You can have the Back Button redirect to any web page you like by setting backButtonUrl (in JuiceboxBuilder-Pro's 'Customize -> Back Button' section).
The value for backButtonURL can be a relative path (relative to the web page containing the gallery's embedding code) or an absolute path (starting with either http:// or https://), for example:

backButtonUrl="http://www.example.com/index.html"

For reference, a list of all Back Button options can be found here.

I hope this helps.

Yes, I agree. It would be better to get to grips with WordPress 5 and new Gutenberg Editor as this seems to be the way forward and WordPress are not going to drop the Gutenberg Editor any time soon.

Your screenshot shows that WP-Juicebox is installed and active and that you've managed to add a Juicebox gallery to your post.
All you need to do now is attach images to your post (using core WordPress functionality) and Juicebox will automatically display them in the gallery.

(1) Click the 'Add Block' button (the '+' in a circle near top-left in your screenshot) to add a new Gutenberg block to your page or post.
(2) Select a 'Gallery' block. (You'll find it in the 'Media' section.)
(3) Click the 'Media Library' button within the 'Gallery' block.
(4) Drag and drop the images that you want to attach to your page or post (i.e. the images that you would like to be displayed in your WP-Juicebox gallery) from your hard drive into the media window.
(5) Wait until the images have finished uploading.
(6) Reorder the images (if necessary) by going to the 'Create Gallery -> Media Library' section (within the media window), selecting 'Uploaded to this post' from the drop-down menu and then dragging and dropping the thumbnails into the order you require.
(7) Close the media window via the cross at the top right. (Do not click the 'Create a new gallery' as this will create a native WordPress gallery in addition to your WP-Juicebox gallery.)
(8) You can now safely remove the 'Gallery' block from the post. (Using a 'Gallery' block is just a convenient method of attaching images to a post.)

WordPress does not make it easy to attach images to a post (or to see images which are attached to a post) but the above method works.

If you find you still have trouble attaching images to a post, then there are a couple of alternatives.

(1) You could use a Flickr account as the source of images for your Juicebox gallery. WordPress would then have no part in the image management of your gallery.

(2) You could choose not to use WP-Juicebox at all and, instead, create a Juicebox gallery on your computer (with JuiceboxBuilder) and manually embed the gallery into your WordPress post using the baseUrl method documented here. Here is an example of how you could do this:

Step #1
Create your gallery with JuiceboxBuilder and save it to a new empty folder named "my_gallery_folder".

Step#2
Upload the entire gallery folder (not just the contents) to the root directory of your web server (using an FTP program such as Filezilla).

Step #3
Create a new 'Custom HTML' Gutenberg block (in the 'Formatting' section) and paste the following embedding code (changing the gallery dimensions and background color if you like):

<!--START JUICEBOX EMBED-->
<script src="/my_gallery_folder/jbcore/juicebox.js"></script>
<script>
    new juicebox({
        baseUrl: "/my_gallery_folder/",
        containerId: "juicebox-container",
        galleryWidth: "100%",
        galleryHeight: "600",
        backgroundColor: "#222222"
    });
</script>
<div id="juicebox-container"></div>
<!--END JUICEBOX EMBED-->

The leading slashes in the paths above denote your root directory so the code above will work without modification as long as your gallery folder is named "my_gallery_folder" and has been uploaded to your root directory.

Incidentally, you can upload your gallery folder to anywhere on your web server as long as the two paths within the baseUrl embedding code (the path to the 'juicebox.js' file and the baseUrl entry itself, pointing towards the gallery folder) are correct.

You'll only see the 'WP-Juicebox -> Manage Galleries' link (shown in my screenshot in a post above) on your WordPress dashboard page (not on an 'edit a post' page such as the one shown in your most recent screenshot).
Just click the 'W' icon (the one in the circle at the top-left of your screenshot) to see the WordPress dashboard menu ath teh left of your screen. The WP-Juicebox link will be near the bottom of the list. (This will not help you to attach images to a post, though... it will only give you access to the 'Manage Galleries' page where you can edit galleries (to change configuration options) or delete galleries.)

That's down to the way WordPress works. The only way I've found to see the images attached to a post (whilst creating or editing a post) is to create a 'Gallery' block, check the images in the media window (accessed via the 'Gallery' block') and then remove the 'Gallery' block afterwards.
Otherwise, you can see which images are attached to which posts in the 'Media -> Library' itself (accessed via the WordPress dashboard).

I hope my notes above help somewhat.

This seems like a Drupal-specific gallery structure type of issue (i.e. a problem building the gallery within Drupal rather than a problem with Juicebox itself).

I'm not sure if you are using the Juicebox Module for Drupal but it sounds like you might be.
I don't know you are building your Juicebox gallery or how you'd get the paths of the images from your Lightbox Gallery into your Juicebox gallery's 'config.xml' file.

As the Juicebox Module for Drupal is an unofficial plugin which was not written by ourselves, I would recommend that you post your query in the Drupal forum where the author of the module (Ryan Jacobs) should hopefully be able to help you further.
He is active and very helpful in the Drupal forum and has a much better knowledge that I have of both the module and Drupal.

An alternative to using the module would be to create a gallery first on your computer using JuiceboxBuilder-Lite and then embed the gallery into your Drupal page using the baseUrl method of embedding following the Embedding in a Drupal Site instructions.
In doing so, you would be able to keep each gallery in its own self-contained folder (helping to keep things organized on your web server).

Here's an example of how to embed a gallery (created with JuiceboxBuilder-Liteon your computer) manually into a Drupal page.

Step #1
Create your gallery with JuiceboxBuilder-Lite and save it to a new empty folder named "my_gallery_folder".

Step#2
Upload the entire gallery folder (not just the contents) to the root directory of your web server (using an FTP program such as Filezilla).

Step #3
Create a new Article, select 'Full HTML' from the 'Text Format' drop-down menu and paste the following embedding code (changing the gallery dimensions and background color if you like):

<!--START JUICEBOX EMBED-->
<script src="/my_gallery_folder/jbcore/juicebox.js"></script>
<script>
    new juicebox({
        baseUrl: "/my_gallery_folder/",
        containerId: "juicebox-container",
        galleryWidth: "100%",
        galleryHeight: "600",
        backgroundColor: "#222222"
    });
</script>
<div id="juicebox-container"></div>
<!--END JUICEBOX EMBED-->

The leading slashes in the paths above denote your root directory so the code above will work without modification as long as your gallery folder is named "my_gallery_folder" and has been uploaded to your root directory.

Incidentally, you can upload your gallery folder to anywhere on your web server as long as the two paths within the embedding code (the path to the 'juicebox.js' file and the baseUrl entry itself, pointing towards the gallery folder) are correct.

I hope this helps (or at least points you in the right direction).

Yes, no problem.
A Juicebox gallery has very few server requirements. Please see here for details.

That is correct. Juicebox does not require or use a database at all.

Hi! Thank you for your interest in Juicebox!
I hope my notes below help to answer your queries (even if they may not be the answers you were hoping for).

No. You must set the thumbWidth and thumbHeight manually (on the 'Images' tab of JuiceboxBuilder-Pro).

With Juicebox-Pro, you can set the thumbnail dimensions (which is not possible with Juicebox-Lite) but all thumbnails will share the same dimensions. This cannot be changed. If images do not share a similar aspect ratio to the thumbnail dimensions, then the images will be resized and center-cropped to fill the thumbnail dimensions.

You could create your own set of thumbnails in an imaging program such as Adobe Photoshop and then swap them for the thumbnails created by JuiceboxBuilder-Pro (if you have a particular set of images which would not suit a center-crop) but this would be a lot of extra work (and all thumbnails in the gallery would still share the same dimensions).

If your gallery uses thumbnails primarily as a navigational aid (and center-cropping would be an issue), then you could choose to not actually show the thumbnails and instead just use thumb dots as shown in this demo gallery.

It shouldn't (and it doesn't for me)! I've just double-checked the Top-Left Alignment demo in Chrome, Edge and Firefox. Resizing the browser window has no effect on the actual dimensions of the gallery, the main image or the thumbnails (due to the gallery having a fixed size of 1000px x 1000px). Making the browser window smaller than the gallery simply crops the gallery (and you'll not be able to see the whole gallery at once without scrolling the web page).
As I mentioned previously, the only way I can make anything in the gallery look smaller is by changing the browser's zoom scale.
I'm not sure if this is what you are doing but it's the only thing I can do to replicate what you are describing.

Just to clarify, that's not something that Juicebox does under any circumstance. Thumbnail dimensions remain constant, regardless of whether or not the gallery itself is responsive. The only way to make thumbnails look smaller is by changing the browser's zoom scale.
Check out this full-page responsive demo gallery . When you change the browser window size, the dimensions of the main image will change (depending on the space available) but the dimensions of the thumbnails will not change. (The number of thumbnails being displayed will change though, depending on the space available.)

Juicebox does not use media queries to switch between Small Screen Mode and Large Screen Mode.
There are more differences between Small Screen Mode and Large Screen Mode than can be handled by CSS alone. (In Small Screen Mode, thumbnails and the main images are displayed on different pages and different configuration options are used when displaying the gallery.)
Juicebox uses JavaScript to check the device/browser being used to view the gallery and the size of the viewport.
If screenMode="AUTO" (the default value) and the gallery is being viewed on a mobile device with a screen whose largest dimension is 1000px or less, then Small Screen Mode will be used (otherwise, Large Screen Mode will be used).

By default, screenMode is set to AUTO and Juicebox will make the decision as to which screen mode to use automatically.
Take a look as this demo gallery (which uses all default settings) in a desktop browser and on a mobile device and you'll see the different screen modes being used.
However, if you like, you can force Small Screen Mode or Large Screen Mode to always be used on all devices and in all browsers by setting screenMode to either SMALL or LARGE in JuiceboxBuilder-Pro's 'Customize -> General' section.

I hope my notes above help to clarify things.
Please let me know if you have any other queries and I'll do my best to answer them for you.

@winglet

As noted above, you can change the color for all gallery text via the textColor configuration option (in JuiceboxBuilder-Pro's 'Customize -> Lite' section).

If you want to change the color of only the image number in the caption area, then you can use the following CSS (changing the color value as necessary):

/* IMAGE NUMBER */
.jb-cap-frame .jbac-number {
    color: #ff0000 !important;
}

For more information on formatting image titles and captions, please see this forum thread.

You're very welcome!
I'm glad I was able to help.

Take care and best wishes!

That's good to hear! Thank you for letting me know.