What I don't understand is why OAuth is rarely talked about in a privacy context, however your OAuth provider knows all the sites you log into and when.
It's a privacy nightmare.
Centralised identity is basically the government... and having some other entity behave the same way is not good.
Though given most people use gmail or outlook, the two main oauth providers (Google and Microsoft) will know anyway
Your OAuth provider can also vouch for anyone who pretends to be you, if they so desire. They can give access to anyone, including themselves.