I use modals 12.3.5 PRO,
and I have one gallery (=directory) that contains *.JPG files (instead of *.jpg) -> file extension in capitals
This works under Joomla 3 but not under joomla 4.
Under Joomla 4 the Popups look strange (fill the whole screen with much white space),
please see yourself:

this is not a big issue I just wanted to let you know ...

with 12.3.6PRO-dev2675710 the described fault is still there

v12.3.6-dev2676083 works fine