You are trying to update user fields before user is even registered using pre-user-registration action. I am not sure, if this is even possible. You can likely use post-registration-action and update user call to set this field to verified.
// Use a post-registration trigger instead
// This is often more permissive with user modifications
exports.postRegistrationHandler = async (event, context) => {
if (event.user.user_metadata?.skipEmailVerification) {
// Use the link above to build your auth0 update API call.
await auth.updateUser(event.user.id, {
emailVerified: true
});
}
};