With authenticated web messaging, can Genesys Cloud detect end-user’s identity attributes?

Yes, but only if the profile scope is set. At the moment the only OpenID Connect Claims that are automatically captured by Genesys Cloud are sub, given_name, email, and family_name, which are then exposed as pre-built variables within Architect inbound message flows as respectively addressDisplayable (sub claim), name (concatenating given_name, email, and family_name). For more information, see Authenticated web messaging attributes.