I installed dbus-broker and the package manager checked the dependencies and removed the unnecessary stuff. After that I applied the dbus-broker services:

systemctl enable dbus-broker.service

sudo systemctl --global enable dbus-broker.service

And then restarted.

Idk if it might break things in mint, so I would be cautious.

Yes, I remember reading about a gtk thing that interacts with flatpak, they said it should not give this error in April, but it seems to still be happening, idk.

Edit: I just saw that you deleted the gtk portal and it worked! So no need to install another dbus daemon.

I had this problem with flatpaks, I changed the dbus implementation to dbus-broker (in endeavouros) and it fixed the issue. It may be the same problem.