I believe this is one of those Google "F it I am going to make this protocol my own way without anyone else's input" which results in security concerns and also Mozilla prioritizes it being a browser more.
Searching serial looks like this is still the case. There are security and privacy concerns over it.
Its using OpenID so yes it would support those. But it would support a lot of others as well. Authelia, keycloak, and authentik are a few examples that are open source and self hostable. Its nice to have SSO for all your services even in a homelab.