Windows 10: Why can't I use my .onmicrosoft account for windows?

So I'm trying to use my .onmicrosoft account for windows 11, but it won't let me, it says that the account doesn't exist.

:)

 

Onmicrosoft

I have just reinstalled windows on my computer. Why can I not login to Windows with my onmicrosoft (Office) password?

 

Remove account

I suggest you backup your personalized files first before removing the account.
To delete an account, follow these steps:

1. Press WIN + X keys and click Command Prompt (Admin) from the menu.
2. Type the following command and press Enter. Replace test with the name of your sister's account. Code:

 

Strange Windows 10 User Account issue.

Unfortunately I had done those steps numerous reboots, it just, reappears for no good reason. The base account isn't even a Microsoft account, it's a local account.

I haven't quite tried the built in administrator account on W10, but so far in my experience on my own computer, the built in account seemed to have absolutely no more control than I did on my own.

It's just strange, I go in, it warns me twice about deleting the account, then it's gone. Reboot, and it's back?

EDIT: Just to specify, both command line and Netplwiz both say only HIS account exists on the computer, it doesn't list this rogue account. This is what I meant in my first post about the fact that even Windows doesn't seem to believe it exists, HALF the time. *Frown