I was having similar problems on a fresh arch install with multiple apps taking upwards of 15 seconds to launch, and the "fix" ended up being to uninstall one or more of the "portal" packages (there are several with names like xdg-desktop-portal-gtk). https://gitlab.gnome.org/GNOME/xdg-desktop-portal-gnome/-/issues/74 and https://bbs.archlinux.org/viewtopic.php?id=285334 for more info.
Could be completely unrelated, but it might be worth a try.