nm-connection-editor should talk to NetworkManager over DBus (via
libnm), so a Flatpak should (in theory) have the same functionalities
as the bare metal one.
Please, let me know if you find regressions in the Flatpak.
For a long time, nm-c-e was hidden in GNOME. That means, there
is not UI path to start the tool, which is undesirable.
On the other hand, gnome-control-center had a dependency on nm-c-e,
so usually you would end up having two network tools. That was deemed
confusing. As solution, nm-c-e was hidden.
We already wanted to do this ([1], [2], [3]), but then there was
pushback ([1], [4]).
The plan was to first make g-c-c independent of nm-c-e ([5], [6])
so that one could install GNOME/g-c-c without nm-c-e. A major part
of that work was splitting out libnma as a separate library ([7]).
We are now ready to do this and revert ([[4]) -- except for example
on Fedora g-c-c still "Recommends:" nm-c-c and nm-c-c gets installed
by default ([8]).