I just set this up today and found that one also must install the xdg-desktop-portal and xdg-desktop-portal-kde packages. I then added GTK_USE_PORTAL=1 to .prof

I just set this up today and found that one also must install the xdg-desktop-portal and xdg-desktop-portal-kde packages. I then added GTK_USE_PORTAL=1 to .profile and relogged.