Well I decided to use CasaOS because I thought it would make things easier, but here it seems to complicate things. As far as I can tell CasaOS provides no way to manually change the docker-compose file (it is all done through the web UI) so I’m unsure how to do step 3 in the docs above.
Seems these are the relevant options: --runtime=nvidia --gpus all
Anyone have an idea of how I can enable these options for my Jellyfin Docker container in CasaOS?