Have you tried non official jellyfin clients? I had issues with the official app on AppleTV as well, so I switched to Infuse. The free app supports most things and I think the paid gives access to additional codecs if I recall correctly. The pro upgrade isn’t too expensive and the app is sleek across Apple devices. Only issue I’ve really had is sometimes if a video is not played to the end (as in, stopped during credits) it still shows up in the continue watching, but that might be a problem on my end.

I think MXPlayer is similar on Android which might be worth checking out.