I am pretty sure that it has to do something specificially with the Steam Flatpak
That is also possible. But then why is it working for everyone else? I used the steam flatpak multiple times today with no issues. I guess you could also ask the same question for the system package issue theory.
How about the package manager version? Is that working? That could give some hints on whether it’s the system or the Flatpak package.
Arch, yes. This is what all the people who had to remove xdg Desktop portal use. How could they remove it if it’s a dependency of flatpak? Maybe they don’t have flatpak.
If you have too much time on your hands, you could try another fresh arch installation on another hard-drive. If it works there, we know it has to be a system package. If it doesn’t, it’s probably the Flatpak.