WORKAROUND: replace gdm3 with slick-greeter + lightdm-settings + gnome-screensaver + numlockx(optionally)
Greeter will auto-appear on whichever screen your mouse is on or moves to, dynamically.
See: https://bugs.launchpad.net/ubuntu/+source/gdm3/+bug/1820423
WORKAROUND: replace gdm3 with slick-greeter + lightdm-settings + gnome-screensaver + numlockx( optionally)
Greeter will auto-appear on whichever screen your mouse is on or moves to, dynamically.
See: https:/ /bugs.launchpad .net/ubuntu/ +source/ gdm3/+bug/ 1820423