Как отключить отображение системных пользователей на экране входа в систему (LightDM)
If your system uses AccountsService, you can not hide a user from the greeter screen by reconfiguring lightdm because it defers to AccountsService. That is stated very clearly in the comments in /etc/lightdm/users.conf.
What you need to do instead is to reconfigure AccountsService.
To hide a user named XXX, create a file named
/var/lib/AccountsService/users/XXX
containing two lines:
[User]
SystemAccount=true
If the file already exists, make sure you append the SystemAccount=true line to the [User] section.