GDM fails to start in Wayland mode, falls back to X11

Running up-to-date Arch on XPS 15 9560. GDM is version 3.38.2. Laptop has Intel and NVIDIA cards, only Intel is connected to display, NVIDIA is kept powered off, proprietary driver not installed. WaylandEnable=false is not set in /etc/gdm/custom.conf, /run/gdm/custom.conf does not get created either (so gdm-disable-wayland is not triggered via udev rules).

It seems like GDM first tries to start the greeter with Wayland, but that fails for some unclear reason, and then it falls back to X11. I've also cleared /var/lib/gdm (gdm user's home directory) to be sure, but the issue still occurs.

gdm.log Attaching output of journalctl -b -u gdm with [debug] Enable=true set in /etc/gdm/custom.conf. Note this line: Gdm: GdmDisplay: Session never registered, failing.

I'm available to supply more info if needed.