Thanks Stephen,
It’s working now, especially after removing firstImageIndex="1"!
I have two types of pages that work!

New 1:
http://lepec.and.co.free.fr/photo/2025gando
galleryHeight="92%" with <header> (I removed the table)
Results on Windows PC >> Perfect in my opinion, the gallery integrates nicely, and with a common top banner, navigation is easy. You can return to the main page by clicking on the icon (cow!)
Results on iPhone (iOS) >> SplashPage appears, but that’s OK, with one click on the chosen image, it brings you straight to the gallery (in Small Screen Mode).

New 2:
http://lepec.and.co.free.fr/photo/2025gandox
galleryHeight="100%" x 100%
Results on Windows PC >> OK, with an improved title (including an image), but no clickable link back to the homepage. Also, on large screens, the thumbnails are far to the left of the photo, the split view is less appealing to me.
Results on iPhone (iOS) >> No SplashPage, it opens directly, responsive view works well.
The advantage is that the HTML code is very very simple, with no styles.css.

I'm still undecided. I guess you prefer... I mean, recommend 100x100 New 1 ;-) ?

Thanks again, really appreciate it

Edit : I added New 1 bis
http://lepec.and.co.free.fr/photo/2025gandoxx
= New 1 with showSplashPage="NEVER"
Results on Windows PC & iPhone >> OK. I have to check with others mobile devices

Thanks, Stephen, for all this advice.
My main takeaway: to ensure this works, my gallery must be the only element on my web page and its dimensions must be 100% by 100%.
I ran two new tests: without a table (92%) and 100-100%.
They all work well on a Windows PC.

Ref:
http://lepec.and.co.free.fr/photo/2025gando
galleryHeight="92%"
<table
Results on iPhone IOS > >> SplashPage

New 1:
http://lepec.and.co.free.fr/photo/2025gandoxx
galleryHeight="92%"
<header
Results on iPhone IOS > >> SplashPage

New 2:
http://lepec.and.co.free.fr/photo/2025gandox
galleryHeight="100%"
Results on iPhone IOS > >> No SplashPage but 1 image!?

For now, I prefer New 1, because I don't have the gallery directly with New 2.
Why or what do you think?

Splash Page Display Issue on Mobile Devices

Hello,
I believe I’m experiencing the same SPASH PAGE problem that vincefx reported back in 2023.

I've been using JuiceBox for several years, and I've noticed that my gallery does not display correctly on mobile devices (iPhone – tested on Safari, Firefox, and Chrome). It works perfectly on a Windows PC, but when I click a link to access the gallery from my smartphone : a fullscreen version of the first image.

The JavaScript seems to load properly (I’ve checked), but the gallery container is replaced by the first photo in the list.

From what I understand, this might be related to how the script is embedded. I suspect you might recommend avoiding the use of a table for layout purposes (may be to be replace by CSS flexbox ?), but before making any changes, I’d prefer to ask.

Thanks in advance for your help!

The link to my last website (I try to do my best with index.html & config.xml ;-) : http://lepec.and.co.free.fr/photo/2025gando/
The link to an older one with the same problem :  http://fabien.photo.free.fr/limousin2024/

Thank you for your help