There are definitely UI inconsistencies across devices, especially smart TVs. Jellyfin on Firestick looks different from Jellyfin on Roku which looks different from Jellyfin on WebOS. Some devices deliver Jellyfin through a thin browser client, and in those cases you get access to a unified design. Outside of that it's a crapshoot as what the app will let you do. Of course, it's a volunteer project (and all my thanks to any maniac willing to develop TV apps), so I don't expect that everything can be easily and neatly unified.

I can't deny that it's sometimes hard to support my users because of this. Someone complains that they're getting movies dubbed in an unwanted language: I can't guarantee that the button to select audio track will look the same on their end when I talk them through it.