Untitled

/**
 * Implements hook_form_alter().
 */
function your_module_name_form_alter(&$form, \Drupal\Core\Form\FormStateInterface $form_state, $form_id) {
  // Check if the form is the user registration form.
  if ($form_id == 'user_register_form') {
    // Add a custom submit handler.
    $form['#submit'][] = 'your_module_name_custom_submit_handler';
  }
}

/**
 * Custom submit handler to auto-approve Gmail.com registrations.
 */
function your_module_name_custom_submit_handler(&$form, \Drupal\Core\Form\FormStateInterface $form_state) {
  // Get the email address submitted by the user.
  $email = $form_state->getValue('mail');

  // Check if the email address belongs to Gmail.com.
  if (strpos($email, '@gmail.com') !== false) {
    // Approve the user registration.
    // You can use the following code to approve the user programmatically.
    $user = $form_state->getFormObject()->getEntity();
    $user->activate();
    $user->save();
    
    // Optionally, you can display a message to the user indicating approval.
    drupal_set_message(t('Your registration has been automatically approved.'));
  }
}