I don't have a static IP adress, so I use Tailscale to connect remotely to my Jellyfin server (located at home).

Jellyfin + Tailscale, the perfect combination.

Uninstall unused flatpak dependencies:

flatpak uninstall --unused

Perhaps the manual is a bit outdated. In recent versions of Docker, docker-compose is installed as a plugin for the docker command. So instead of using docker-compose up -d, try using docker compose up -d (note the white space between "docker" and "compose").