The Jellyfin Server plugin is now available in the beta channel of the plugin store. Starting from v0.1.3, the plugin will not install and run Jellyfin through Docker. Previous versions are not considered to be “stable” and known to fail on rpi4. If you have a previous version installed, please uninstall it first before installing the current one, followed by restarting Volumio (note that you will lose any Jellyfin config, playlists and favorites in the process - sorry about that; future versions will keep them intact on update).
Thanks @balbuze for testing this plugin and putting it in the store. Same goes for my other plugin submissions.