Continuing the discussion from Wayland monitors.xml interaction with xorg monitors.xml:
I tried to follow arch linux - How to let GDM shares monitor configure with GNOME? - Unix & Linux Stack Exchange to configure which monitor is primary, etc. But that did not help.
This was their suggestion:
cp ~/.config/monitors.xml /var/lib/gdm/.config/monitors.xml
What is the current state of configuring the use of monitors by GDM?