Parallels Desktop 20 for Mac updates summary

I've updated Parallels Desktop to Version 20.3.0 (55895). After the installation of the Parallels Toolbox Update in my Windows VM (I'm on Windows 11 ARM on a MacBook Pro M1Max), I can't boot anymore. It says: No OS installed. My VM was working fine for the last years, so no clue what happened. Glad I had a Time Machine Backup, but also the Backup stopped working after the Update. Any suggestions?