Error when retrieving webform elements with a text format field

One possible solution is to adjust the output format of the 'About' URL for the 'text_format' field.

function your_module_process_text_format_field(array $element, FormStateInterface $form_state, array &$complete_form) {
  if (isset($element['format']['help']['about']['#url']) &&
    $element['format']['help']['about']['#url'] instanceof Url) {
    // Normalize the URL object to a string.
    $element['format']['help']['about']['#url'] = $element['format']['help']['about']['#url']->toString();
  }
  return $element;
}