Hello, thank you for reaching out to Microsoft Q&A.
Could you please confirm whether you’re signed in to your computer with a local account or a Microsoft account?
- Press Windows + R, type netplwiz, and click OK.
- In the list of users, select your username and click Properties.
- In the Full name field, enter the name you want to display on the lock screen.
- Click Apply, then click OK.
Sign out and sign back in if the new name doesn’t appear immediately. (or) Restart your computer.