Funny thing now is that I installed another GPU via the M2 slot - at first Windows detected the new GPU but I had to reinstall and now it is all messed up.
Screen stays black I can't boot from the Boot ready USB Stick - I have no idea how to fix this besides reinstalling from scratch. Did you guys encountered this already?
Edit: Windows is not fully booting up as I am not able to connect with Teamviewer. I suspect this is a graphics driver issue, searching for the topic returns many hits but nothing really useful.
Ok disabling 4G - cleaning the drivers, reinstalling them patching them and turning on 4G again solved the issue. Just Windows that wanted to go nuts. Now the additional card in the M2 slot also works like a swiss clock
Thanks everyone for the help - appreciated!