OpenID Connect actually has all the machinery needed to support federated login as part of its dynamic discovery and dynamic registration specifications. The issue is that absolutely no one uses them or implements them.

Smaller tech companies don't want federated login to happen. They are, as a rule, far to happy to rely on the SSO tax to up-sell enterprise customers. The major authentication companies don't want federated login to happy because it invites more competitors and threatens their absurd margins.

Until someone manages to solve the business side, no amount of improved technology will change a thing. I'm pretty sure the few small interoperability gaps OpenID Connect has could be corrected in a matter of months if the stakeholders actually cared.

OpenID started its life as an attempt at a federated login standard.

From vague memory, the other stuff in OpenID Connect was layered over the original OpenID identity verification part.