Hey Jose,
Google OAuth2 is working here on Meta, as well as our demo site try.discourse.org (you can test either/both if you’d like), so I don’t think it’s a Discourse issue. My suggestion would be to go back in and triple check every value you configured, both on Google’s side and within Discourse site settings. If it’s still failing, try starting from scratch with a new GoogleAPI project.
Also, for those who can’t currently sign in, assuming they signed in at least once previously, assuming you have user/pass login enabled, have them go through the password reset process. That’ll let them log in with their newly created password. Once Google is working again, they can go back to logging in that way.