Flatpak is designed to run inside a desktop session and relies on certain session services, such as a dbus session bus and, optionally, a systemd --user instance. This makes Flatpak not a good match for a server.
However, the build features of Flatpak run fine outside a session, so you can build things on a server.
Die Flatpak-FAQ aber:
Can Flatpak be used on servers too?
Flatpak is designed to run inside a desktop session and relies on certain session services, such as a dbus session bus and, optionally, a systemd --user instance. This makes Flatpak not a good match for a server.
However, the build features of Flatpak run fine outside a session, so you can build things on a server.
(einer der größten Schwächen, die ich bei meinem vergleichenden Blick gefunden habe; abgesehen davon, dass die Grundidee an sich halt polarisiert)