It was something about adding group to my docker compose file that did the trick.

Ah yes, I do remember something about certain distros limiting access to /dev/dri/renderD128. So maybe adding the group gave the docker process the necessary permissions? I am not sure, just making guesses right now. Super glad you got it working though!

Next issue, Swiftfin for Apple TV needs quite a bit of polish

Yeah, this is definitely one of the areas Jellyfin needs to catch up on. Their app support is a bit buggy, if not entirely unavailable on certain SmartTV platforms. Definitely an adjustment. I use the Jellyfin chromecast app, and its also buggy with subtitles. Every time I seek, the subtitles get duplicated. I am sure this will all get ironed out over time.