This is to create a user that does not show in Control Panel → User Accounts or on the Sign In Screen

net user UserName PassWord /add

net localgroup Administrators UserName /add

UserName and Password are replaced with your chosen values

https://www.windowscentral.com/how-hide-specific-user-accounts-sign-screen-windows-10

1. Use the Windows key + R keyboard shortcut to open the Run command, type regedit, and click OK to open the Windows Registry.
2. Browse the following path: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon
3. Right-click the Winlogon, select New, and click Key.
4. Name the new key SpecialAccounts.
5. Right-click the SpecialAccounts key, select new, and click Key.
6. Name the new key UserList.
7. Inside of UserList, right-click, select New, and click DWORD (32-bit) Value.
8. Name the new DWORD key with the name of the account you're trying to hide.
9. Double-click the new DWORD key and make sure its data value is set to 0.