It works. Of course showing no pictures but the file browser opens normally.
Ok, so we are slowly getting somewhere, now try this: Download the latest Files Gallery index.php again, but now overwrite the existing /files/index.php
in your X3 dir.
https://cdn.jsdelivr.net/npm/files.phot ... /index.php
This will essentially upgrade it from 0.5.7 to 0.7.0, but keep the existing config with login. To me, this looks very much like 0.5.7 is not working for you on iOS, and newer version 0.7.0 does. Why, I don't know, because 0.5.7 works fine on other iOS devices from other locations.