As a Windows user, I've never been able to edit the text in the 'Gallery Folder' box.
I've always had to click the 'Browse...' button and navigate to a pre-existing folder (or create a new folder within the pop-up 'Save Gallery Folder As' dialog window).
In fact, I've just checked and the 'Gallery Folder' text is, indeed, set to be non-editable so if you've previously been able to edit it, that's rather strange and perhaps a bug within AIR.

One other Monterey user has reported a similar issue.

Could you please let me know at exactly what point in the process the application freezes?
It might help in troubleshooting the problem or, at the very least, I can log a bug report with the developers.

Is it when you try to select a pre-existing folder or create a new folder in the 'Save Gallery Folder As' dialog window?
Are you trying to save a gallery to a network drive or a folder which is being synced to an online file sharing service such as Dropbox or Google Drive?
Does there appear to be a pattern to when the application freezes?
Have you found a workaround which may be inconvenient but works consistently?
How often (as a percentage) would you estimate that the problem occurs?

My own workflow pretty much involves just saving a gallery named 'juicebox-gallery' (the default name) to my desktop and then renaming and moving the gallery folder as necessary.
I realise that this might not be convenient for everyone but if you are not already doing this, then it might be worth trying. It doesn't involve clicking the 'Browse...' button at all (or editing the non-editable text).
If your 'Gallery Folder' text has changed from its default value and you'd like to revert to the default value, just delete the following folder (with JuiceboxBuilder-Pro closed).

/Users/Username/Library/Application Support/Adobe/AIR/ELS/JuiceboxBuilder-Pro

It should be fine to do this (I've just done it myself on my Windows system... I don't have a Mac) but it might be wise to just move the 'JuiceboxBuilder-Pro' folder out of the 'ELS' folder (onto your desktop, temporarily) in case anything goes wrong and you need to reinstate the folder at a later date. I really do not foresee any problems with this but it would be better to be safe than sorry being that you are unfortunate enough to already be experiencing issues.

Looks as though it is exactly the same issue!

I have only just received my MBPro M1 and Apple's Software Updater indicated that I should update to 12.1 — which I immediately did.

Then, having checked that my printers and scanner would work in 12.1, I then updated my MacMini M from Big Sur to Monterey 12.1 as well.
JBPro had been running perfectly well on the Mini until I upgraded its Mac OS.

And the symptoms do match the Bug: the first time that I needed to use the Browse button was O.K. but since then I perpetually experience the Freeze issue.

From your linked thread, it sounds as if Harman Air are aware of the issue and are currently working on a fix.

If you are urgently looking for a solution, you could perhaps try extracting the runtime files from the new SDK that Harman has just released and manually replace the existing runtime files on your systems.

Download either of the MacOS SDK files (both contain the same runtime files) from this web page: https://airsdk.harman.com/download
After extracting the zip file, you'll find the 'Adobe AIR.framework' runtime files inside the 'runtimes/air/mac/' folder.
The location for 'Adobe AIR.framework' should be /Library/Frameworks/Adobe AIR.framework
This is untested but should hopefully work OK.

Please let me know how you get on if you choose to try this.
Thank you.

Otherwise, deleting the 'ELS/JuiceboxBuilder-Pro' folder (as I noted in a post above) to revert the 'Gallery Folder' text to its default value should enable you to save a gallery to a folder named 'juicebox_gallery' on your desktop (where you can then rename and move it as required) without having to use the 'Browse...' button (which currently invokes the faulty file chooser) at all.

I'm sorry to hear that you are still having such problems.
I swapped the AIR framework files on my Windows system (C:\Program Files (x86)\Common Files\Adobe AIR) with the new runtime files from the updated Harman AIR SDK with no problems or adverse effects at all, hence my suggestion for you to try it on your Mac. (I experienced no problems adding multiple images, no speed degradation populating the 'Images' tab, no problem opening existing galleries and no problems with the 'Save Gallery Folder As' dialog window.)

Until the new runtime is released, you might like to just revert to the current AIR runtime (v33.11.533) which you can download from here: https://airsdk.harman.com/runtime
At least then you can save each new gallery to a folder named 'juicebox_gallery' on your desktop and stay away from the 'Browse...' button in the hope that the new runtime will fix it.

From your description of how things stand at the moment, I'd recommend a complete uninstall of both JuiceboxBuilder-Pro and AIR. When the time comes, you should be able to use the new runtime installer to upgrade AIR (on top of the old version, without having to uninstall or reinstall anything further).

It seems that my Bugs are related so I have added my comments to the GitHub discussion

To follow-up on the AIR issues:

I followed your advice and wiped all parts of both JuiceBoxPro and AIR completely off all of my Macs. Doing that has resolved nearly all of the problems which I was experiencing.

The real key turned out to involve removing every particle of Harman AIR from the machines (by using their Uninstaller) before loading their latest version of AIR.

I followed the total removal of all things AIR with  making clean installation of JBPro.

The result is that:

I can now insert multiple files from the Image Panel’s Browse for images.

JBPro now populates the Images Panel very quickly again.

Galleries will Save to default the 'juicebox_gallery' directory.

The Save/Browse button does now shows the “New Folder” button again but if I open "Browse" I still get a Freeze so this issue obviously still awaits a fix from Harman.

The Config issue was being caused by a Browser setting (which I have now fixed as I described in another topic).

So JBPro is now entirely workable again for now in both Mac OS Mojave and in Monterey — just as long as I don't hit that "Browse" button in the Save area.

Harman has just released a new AIR runtime (v33.1.1.743) which should hopefully resolve the Mac file dialog issues.
Here's the relevant entry from the AIR SDK release notes:

You can download the new AIR runtime from here: https://airsdk.harman.com/runtime

Please let me know how you get on. Thanks!