How to remove a user from the list on the login screen

To permit the sharing of files I need to add a user to my Win 10 PC with administrator permissions. I do not want anyone attempt to login using this user name but it appears in the list on the login screen. I have read a number of other posts where they refer to modifying the registry specifically modifying the entry in Winlogin to implement this.
I have searched the registry but cannot find this key or value anywhere.
Where is this entry and what do I have to add to remove a specific user from the list of users on the login screen?

Ummmm.......every Windows computer should have at least one administrator account on it. If you don't have an administrator account already on that computer, you are extremely limited in what functions you can perform.

And, if you don't already have an administrator account on that computer - then how do you expect to add one? A standard user without administrator privileges cannot add any other accounts to that computer.

Thanks to both for taking the trouble to reply, but you misread my original posting.
I of course have an administrator account, the problem was I wanted to add another but not present that username on the login screen.
I have read again some of the posts that I referred to and realised I had made a mistake I was searching for the wrong key value, winlogin instead of winlogon. Having spotted my mistake I have used the correct key value in the registry and have the setup I desired.

Why do you need a second administrator account to share files? Standard users can access shared files if the permissions are set to allow that user to access them.

It is my interpretation of what will be required when we upgrade to 2018 creators update (1803).
This update will remove the HomeGroup. I have tried to set up a method which will use windows credentials to allow access to files on a PC on the same LAN. This needs a username and password to access the target machine's files.
Does that explain what I am doing and why or have I got it all wrong. I have 2 PCs, A laptop and 8 Virtual machines all running Windows 10 and 2 running Windows 7 on the same LAN one of the virtual machines is running the insider preview Fast build and another the Skip ahead build.
By creating a user with administrator's authorisation on each specific target machine that can be used by a different machine to access the files on the target machine.