I have a login.gov account. Needless to say I'm not a US citizen, and the IRS should not cut me a refund check.

ID.me supports WebAuthn (or maybe U2F? In this context it doesn't matter) but importantly it does identity verification so it can determine whether I am a US citizen, whether I'm a tax payer, and if so which one.

Now, perhaps the US Federal Government should own the capability to do that instead of a private company. But, so far as I can tell, they do not and login.gov is not such a thing.