@ringo32 thanks for that script. I played a bit with it and I’m pretty sure it will work. I Just think there has to be an error somewhere because it worked on ubuntu with gnome?!
yes I use gnome-control-center.
The external monitor is connected permanently via mini dp.
So I startup my laptop whatever configuration is activated right now I change it to single display external monitor.
On next startup/reboot this configuration is lost. Interesting thing is it’s either single display - internal monitor or join display.
Hope this makes it clearer!