Saved from https://www.drupal.org/project/recaptcha/issues/2213337

modulehook.php

function myModule_element_info_alter(&$type) {
  if (isset($type['captcha'])) {
    $type['captcha']['#after_build'][] = 'myModule_after_build_process';
  }
}

function myModule_after_build_process($element, $form_state) {
  $element['captcha_widgets']['recaptcha_widget']['#suffix'] = '<div><label class="hide" for="g-recaptcha-response">Recaptcha response</label></div>';
  return $element;
}