Hi , you got any update about this already known issue please? this issue is very problematic. As others, when trying to remove or edit existing permissions(here the "Modify" right to 'authenticated Users") it deletes all permissions on the drive, so the system becomes unbootable.
It used to work in 1909.
Build is 20H2 19042.508
Here is the powershell i use (doing it with the system account)
$ACL = Get-ACL -Path "C:\"
$AccessRule = New-Object System.Security.AccessControl.FileSystemAccessRule("NT AUTHORITY\Authenticated Users","Modify","Allow")
$ACL.RemoveAccessRule($AccessRule)
$ACL | Set-Acl -Path "C:\"
Can't even see the permission with system account :

thanks for updating