This plugin is built to work with standards-compliant OIDC services. That means the email should be returned in an “email” field.
If you check the “Azure B2C” section in the first post of this topic, there are some community-provided instructions for setting up a “custom policy” which puts the email address in a standards-compliant location. I’m afraid I’m not familiar enough with Azure B2C to know whether that will work with the “user flows” feature.