Thanks Ralf for your commitment to your masterpiece. Today I have finally enjoyed my first session with the virtual monitor, what a cool feature!
Initially my system did not work. Game crashed/freezed, openxr init error in steamvr mode, black screen in virtual monitor.
Solved it by patience, trial and error, reinstallation of steam vr, reinstallation of Windows Mixed reality ànd (for you not a surprise) closing my antivirus programm.
I hope this is usefull feedback for other struggelers. Hold on, it should work and it’s worth the effort!