I'm using Windows 10 Pro (x64) (10.0.19044.1620). The problem starts right after installing the whole system freshly without any other security software.
I have two other systems with Avast Free (Windows 11 and Windows 10 Home (both x64)) where this problem does not occur.
When I tried to uninstall Avast from my main system, I was told "Installation is already running". Could it be, that there is a Avast installation process running all the time in the background that disturbs the whole system?