Testing really is for testing. If you like to tinker and don’t mind the occasional breakage, testing can be great to help the project by trying out newer software and reporting bugs. Otherwise, stable with backports and/or flatpaks if you need newer packages will be a lot more relaxing.

You can pretty much set it and forget it with Debian. If memory serves, Jellyfin is available through extrepo, so super easy to set up.