Well that’s a shame. I’m sort of half-assedly using syncthing to backup my photos from my phone to my server, but mostly I rely on immich. I never really got the hang of using syncthing with my phone.

Masochism, paranoia.

Another vote for Debian, and I’ll suggest you go ahead and install Jellyfin directly rather than messing with Docker.
https://jellyfin.org/downloads/server
I’d been running JF under Docker on my NAS, but when I moved to a new server I decided to just install it directly and it hasn’t been any problem at all. You’ll get a notification when it needs to be updated and it’s just a few clicks to do so. You won’t have to fight with Docker to get hardware acceleration working - which isn’t to say it won’t be a PITA, but it’s one less layer of complication.