As a Google Plus (Google+) SSO (OAuth) user with Knack, you likely received an email on January 29th from Google alerting you to this shutdown on projects directly requesting the "plus.me" scope.
Knack was not actively using any details in this "plus.me" scope so we have removed any reference to this in our code, which includes removing the “Plus” name on the Builder set up page as shown in the below screenshot. Knack uses the Google `https://www.googleapis.com/auth/userinfo.email` which is not in the Plus umbrella, so it won’t be deprecated. Everything that we use to inform our SSO system comes from that scope.
This means that for your SSO setup with Knack, there is no action you need to take to ensure your authentication continues to work. You should not notice any change when logging into the Live App with this authentication.
Please reach out in the in-Builder messenger or with a note to email@example.com if you have any questions on this. Thanks!