Windows 10 Pro
Version 2004 (OS Build 19041.388)

In an elevated command prompt

Trying to delete C:\Windows.old getting access denied

Also got "The data area passed to a system call is too small." while running cacls

Commands to run to delete C:\Windows.old

takeown /f C:\Windows.old /r /d y
icacls C:\Windows.old /grant administrators:F /T
attrib -s -h -r C:\Windows.old /s /d
rmdir C:\Windows.old /S