Another yak shaved and this time thanks to the internet! It seemed I could not get my external monitor position to persist and my poking around DBUS and dconf did not yield anything. Instead the Red Hat documentation solved all my problems (for now), let’s see what happens when I add another display to the mix with a different positioning!

The solution boils down to persisting your personal display configuration, found at ~/.config/monitors.xml, to /var/lib/gdm/.config/monitors.xml. Remember to change the owner and group so that GDM can read it.

cp ~/.config/monitors.xml /var/lib/gdm/.config/
chown Debiam-gdm:Debian-gdb /var/lib/gdm/.config/monitors.xml

Now it persist across reboots and docking!