It uses GDM3.
I use LightDM on Zorin OS Lite, thereby avoiding this trouble. Gnome removed the User List Order functionality in GDM (Gnome Display Manager) shortly after the release of version 3.
Here is a thread discussing some work-arounds:
There doesn't seem to be a cure as what used to work appeared on the internet; was spotted by Gnome devs; and Gnome devs promptly went in and disabled those techniques.
Two threads popped up in one day that really show why I do not use Gnome. Even Microsoft is not as controlling with Windows OS. Windows is mostly annoying and invasive. Gnome seeks to Dominate the user.