Suppose WebAuthn was the standard authentication scheme everywhere. People used a series of tokens (Yubikeys, phone apps, etc.) with private keys which they use to authenticate to services. The government runs a department where you present them proof of your identity and the public keys from your Yubikeys/whatever, and they would publish a cryptographically signed electronic message which read the equivalent of "the owner of the private keys associated with public keys a, b, and c is a real person"). Then, when you signed up for an account at Twitter, or wherever, they could quickly check that published list and know that you where a real person.
Advantages, you own your own private keys and completely manage your online identity. The government doesn't have any control over where you log in, or who you sign up for accounts with. Also, you can remain anonymous to the site you sign up to. They can check that you're a real person and only signed up once, without actually knowing your real name or other details.