do a takeown /f c:\testfolder123 /r /d y
u will see it is a user on the computer, the way win10 uses permissions is spooky and mysterious, but if u were trying to become the owner, as your true user profile that u made when installin windows, u need to takeown, and certain things break unelss u icacls trustedinstaller to them.
anways workgroup\desktop is not actually the user profile that is your domainname\username but when u takeown, like i say, it shows that file are now owned by the workgroup\desktop. so it may be an administrators group and not the user...