After updating my system about two weeks ago, I noticed certain GTK programs such as Nautilus, file-roller, and the calculator along with others like Firefox and Thunderbird have been slow to start (for example, the calculator takes upwards of 25 seconds to start), and I can’t figure out why. I assume it’s an issue with a GTK component, but I don’t know where to begin to diagnose the problem.
Apparently, it can happen on both, Gnome and KDE, commonly when flatpak is installed.
If one is in need of any xdg-desktop-portal (for varying reasons, see link) a current, recommended workaround is using xdg-desktop-portal-gtk instead of the Gnome or KDE versions!