You can sign-in as a non-government user (though they also have CAC support for federal govt users). There's built-in document/identity proofing as well but there are some extra requirements to get that enabled on an application.

You do need to be working with the government to integrate with Login.gov though (but it's just OIDC on the backend)

That is perfect! Just need it to be opened up a little so that places like Google can enable it as a Lyn optional primary login.

It's used to manage your Global Entry membership.