In discourse “SSO” means this protocol: Setup DiscourseConnect - Official Single-Sign-On for Discourse (sso) (we are working on renaming it to DiscourseConnect… because it’s super confusing at the moment!)
To use openid-connect, do not use enable_sso or sso_url
If openid-connect is the only enabled login method, then sending the user to /login should start the authentication flow.