Is there a way to limit user login/creation based on DOMAIN

…found the solution.

This setting is NOT in the plugin itself, but within the OAuth settings you will need to create when creating the intermediary Google app that processes the authentication request.

In case anyone meets the same problem:

You can set the user type to “Internal” in your Google App on the OAuth Consent Screen. In such a case, Google itself will not allow authentication.

If it is needed to extend this email domain limitation to other providers, then that can be achieved with custom coding, as seen here:
https://nextendweb.com/nextend-social-login-docs/backend-developer/#prevent-registration
In the above example certain domains are blocked, so instead of that the logic needs to be reversed, to only allow certain domains. However, please note that we cannot help with custom coding.