I bought a 4k projector recently to use for a home theatre which came with AndroidTV. I have a small collection of 4k movies and shows that I wanted to enjoy, but my PC was on a different floor from my projector. I had used Plex a long time ago, and looked for an open source alternative and found JellyFin. It took like 20 minutes to get set up and start watching my content on my projector. The JellyFin AndroidTV app auto-discovered the server running on my PC, and it also supports streaming HEVC encoded content natively, which the web browser client on Firefox and Chrome doesn't seem to yet [1]. When I streamed HEVC content in the web browser client, the server was transcoding it on the fly, which was nice but it was sending my PC to 100% CPU. The library organization features are probably not as good as Plex's, but they are good enough for me.
[1] https://jellyfin.org/docs/general/clients/codec-support/
replies(2):