KDE: How can I run kscreen-doctor on startup before login (to disable my external TV screen from showing login dialog)?

Hi all!

In addition to my monitor, I have a TV screen that I don’t use very often. I would like to only enable it as a display on demand via a script which also launches other gaming stuff on that TV. From disabled state, this works fine with “kscreen-doctor output.HDMI-A-1.enable”.

However, when I shutdown the system, the screen is always enabled on next boot and displays the login screen.

Is there a way to run something like “kscreen-doctor output.HDMI-A-1.disable” on boot, or before the login screen is setup? Or any other way to disable the output and enable it later with a command?

I have tried following sddm documentation and placing a file in /etc/sddm.conf.d/ which contains
[X11]
DisplayCommand=kscreen-doctor output.HDMI-A-1.disable

…but this does not seem to get triggered. Replacing the command with “/bin/touch /tmp/testfile” does nothing so I guess this never gets executed.

Any ideas on how to run stuff on boot/before login?