Love a good hack. But in this case, I just use LibreELEC (kodi) and call it a day :D
I haven't used it much myself. How well does it work with streaming services? It seems like it's designed to be really good for offline content.
Being able to play media from Jellyfin and other locations like YouTube, samba shares, etc is why I tend to use Kodi. I’m not stuck with one server/service.
No more transcoding and/or demuxing subtitles on the server
Also the more mature/retro UI, although you can skin it like Jellyfin’s web UI or like yet another streaming service if you prefer