I would like to note, that I have to set:
“xset dpms 00 00 00”
So that the screensaver does not interfere with EXT-screen.
once I set the timeout for EXT-Screen back to 120000, the dpms was set to “60 60 60” and when the screen would go to sleep it would require keyboard/mouse input to wake up.
xset dpms 00 00 00 solved that issue.