Last October I did a presentation at the Microsoft Power Platform Conference in Orlando called Power Pages and Azure AD B2C: a deep-dive and advanced scenario's. It went great, it got real good interaction and feedback afterwards. Some Microsoft people were in attendance too, and they used my session (amongst other sources) as an inspiration for their blog post Identity Strategy for Power Pages.
It's the blog post I should have written about that session, but I'm happy they did it and it's finally out there! Go read it, it'll clarify a lot regarding authentication flows within Power Pages.