Hmm, I know at one point GNOME/GDM locked out Wayland for Nvidia cards - but that hasn't been the case for a while (and possibly was distro specific).
Is there any output from:
cat /etc/udev/rules.d/61-gdm.rules
cat /usr/lib/udev/rules.d/61-gdm.rules
Oh wow, I didn't know about Kandalf and KDE valley, that's awesome!