I have the same problem.
Can someone please confirm that using domain from freedombox.rocks means that Xmpp calls don’t work outside the home network?
It might be a long shot, but it has suspiciously common similarities with my post about TTRSS. There picking the second option (although the same) made it work. In plinth → apps → coturn I get the same two choices, but in this case picking the second option results to
Setting unchanged