FINAL SOLUTION

Since this annoying bug seems to reappear from time to time on Windows 10 (1909, 2004+), I've just found a better and PERMANENT easier solution for this annoying issue.
When you...

Fixed!

I did in this sequence:

export as AllFolders.reg
HKEY_CURRENT_USER\Software\Classes\Local Settings\Software\Microsoft\Windows\Shell\Bags\AllFolders
deleted whole...

Looks like the Quick Access logical "object" is unknown to Windows: typing its name "Accesso rapido" this gets searched on the Net instead of opening Quick Access folder! Not sure if this is normal...

I have a strange problem with Quick Access view:
all of a sudden files are displayed as in every other folder in a single list, and I can't select By group etc. to restore original mixed view:
...