Also Nvidia Contol panel -> System Information -> Advanced Optimus = No
So this means to run your screen throuhgh the deticated graphics card the integrated graphics card has to be disabled.
This was possible when i first got the laptop, and it is not possible anymore, not sure what happened.
I was also able to find the resizable bar enabled before, this is also gone now.
So I am almost 100% sure the MUX switch is broken at the moment.