inferAdditionalFields
What is the purpose of inferAdditionalFields (this is mostly rhetorical) because the returned user object from signin email doesn't have additional fields even if specified and if you don't put inferAdditionalFields in your client config the fields are added by default to the user returned in the session.
I am confused on the purpose because it doesn't seem to do anything. I am likely doing something wrong somewhere.
I am confused on the purpose because it doesn't seem to do anything. I am likely doing something wrong somewhere.

Solution
I'm good. The documentation helps:
https://www.better-auth.com/docs/concepts/typescript#inferring-additional-fields-on-client
https://www.better-auth.com/docs/concepts/typescript#inferring-additional-fields-on-client