It use to use my own identity provider quite a bit, but every website that use to take OpenID no longer does. OpenID Connect is just a modified OAuth and even fewer website that custom OpenID Connect.
Stackoverflow dropping it pretty much put a nail in the coffin.
OpenID may not be particularly common in consumer-facing services, but it is very much still in use for business applications. Almost every web application I use for work handles authentication through my G Suite account.
This is probably easier for the business case, where you can guarantee that everyone has an account from the same provider. Less so when some of your users want to use a Google account, some want to use Facebook (which isn't actually OIDC and requires its own separate implementation), some want to use Microsoft, etc. Like any complex open standard, the completeness and correctness of implementations vary widely, and supporting many different implementations is a pain even if 90% is the same. I'm reminded of my time working with different IPSec implementations.
https://penguindreams.org/blog/the-decline-of-openid/
It use to use my own identity provider quite a bit, but every website that use to take OpenID no longer does. OpenID Connect is just a modified OAuth and even fewer website that custom OpenID Connect.
Stackoverflow dropping it pretty much put a nail in the coffin.