Hello,
I finally will stop that search as I don´t expect to find the solution on a short term. It is only for presentation purpose, perhaps I will create a static site if necessary.
What I finally tried was to update from 2.7.7 to 2.8.8 without updating the gallery before, but this shows the same result. I will stay on 2.8.8 and desired PHP 8.3, that´s it.
Thanks again for your support. Regards, Marco.