IMHO validation should be done at the application level. Because it reduces the processing load on the back-end and validating values such as email is simple to do with regex patterns. Not to mention that besides having to create a whole new logic, it is necessary to add an error handling in GraphQL for that. Which is an extra code to maintain.
At the server level, I would just check if the email already exists(the user register).
If you notice formik is done for integration with the UI. I personally find it a mistake to want the database to do all the work. We should recommend practices and not force different functions like typo checking. I think it fragments and disrupts the main function of the DB. Which is to be a DB.
Cheers.