@Dihedric ,
Change Display Session to X11 at login screen (left-down)
xrandr | grep -w connected
su
kate /usr/share/sddm/scripts/Xsetup
and add lines (modify them according to xrandr | grep -w connected)
xrandr --output DVI-1 --off
xrandr --output HDMI-1 --off
Save it and log-in into Wayland.
With arandr try to activate DVI-D-1 and HDMI-A-1
(this part was not easy for me) As you see wayland and X11 names are different.
Plan B
Read what Der Doktor wrote but for sddm it did not work for me.