I don't normally use that app but I figured I could do a quick test for you - the stable version (0.15.3) does not seem to work on my end. It does connect to the Jellyfin server (10.11.1) but nothing loads after that.

It doesn't look like findroid has had any stable releases in over a year so it may indeed be showing some incompatibility issues.

EDIT: Re-tested, it does seem to work as long as you have video libraries enabled on the Jellyfin user (e.g. Movies/TV). My earlier test was with a Jellyfin user that only has Music enabled, I did not know Findroid does not play music. (most of my Jellyfin mobile use is for music)