forum_form_taxonomy_term_form_alter

forum_form_taxonomy_term_form_alter(&$form, FormStateInterface $form_state, $form_id)

function forum_form_taxonomy_term_form_alter(&$form, FormStateInterface $form_state, $form_id) {
  $vid = \Drupal::config('forum.settings')->get('vocabulary');
  if (isset($form['vid']['#value']) && $form['vid']['#value'] == $vid) {
    // Hide multiple parents select from forum terms.
    $form['relations']['parent']['#access'] = FALSE;
  }
}