When you install and configure the NixOS with Gnome from minimal image, it is possible that you will not see the existing user(s) in the login screen. It expects you to type your username and password. I know it is not a big deal. But, it is annoying.

This is because the user you configured in your configuration.nix file, somehow, is identified as a system user. So, it is not shown in the login screen.

To change this, you need to edit the SystemAccount field in the /var/lib/AccountsService/users/<your-user> file.

Note you may need to switch to root user to edit this file. In my case, trying with sudo vim xxx did not work because the file was owned by root user. So I didn’t have the permission to even read the file let alone edit it.

sudo su
vim /var/lib/AccountsService/users/<your-user>

You should be looking at something like this:

[User]
...
SystemAccount=true

Change SystemAccount to false and save the file. And do this for all users you want to see in the login screen. Now, you should be able to see your user(s) in the login screen.