There are two main account types for signing into a personal Windows PC:
A local account. This account exists only on that computer. The username and password are stored locally and are not connected to Microsoft’s online services. Example: a username like “John” or “Admin” with no email address attached.
A Microsoft account. This is an online Microsoft identity such as Outlook.com, Hotmail.com, Live.com, or another Microsoft-linked email address. When you use it to sign into Windows, the PC still creates a local profile on the machine, but authentication is tied to Microsoft’s online account system and can sync settings, passwords, OneDrive, Store apps, and other Microsoft services.
In your original description, the system is likely showing a local account first at boot while your preferred Microsoft account is still available as another sign-in option.
You most likely have two accounts on the PC: A local account and a Microsoft account.
Windows is currently remembering the local account as the last-used sign-in and showing it first at boot.
To fix this, press Windows+R, type netplwiz, and press Enter. Make sure “Users must enter a username and password to use this computer” is checked. Click OK and reboot.
Then fully sign into the Microsoft account and restart again. Windows will often begin showing that account first.
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hth
Marcin