Some programs did not work for a while - no file menues opened, no viewers where launched, etc. GUI not working.
The problem?
xdg-desktop-portal-gtk.service was not configured workable.
The env-var DISPLAY needed to be set inside the service-file.
The program developers may blame the user of their software to not have set up the system correctly - not their fault!
But you know what?
I consider developers who don't check return values and don't inform the user about problem(solution)s idiots