I run Jellyfin on Raspberry pi and access it with Android app. The main issues I have with the app are:

1. Subtitle management is a total pain. Sometimes it doesn't show any subtitle toggle, sometimes it does. There isn't an option to switch between different subtitles. Adding an external subtitle file on the fly via the app never works for me. One approach that almost always works is to download the subtitle file, rename it to match movie filename, trigger a metadata refresh for the file/library (this requires switching from library view to dashboard view and back so certainly has friction). Also, if you start a movie directly on Chromecast, subtitles don't show even if they have been chosen. However, if you start the movie with subtitles "ON" on the app and THEN stream it via Chromecast, subtitles show up on the TV.

2. Sometimes it has issues with Google Chromecast (puck connecting to my LG OLED TV via HDMI port). I have had better luck with the in-built Chromecast feature of the TV.

The Pi isn't mega snappy when it comes to the lag between button press to actual playback start/end of seeking but it generally works fine once the stream starts playing.

I didn't pay a dime for it so this is not throwing any shade on the Jellyfin team - I am grateful for their work.