public function set_404() {
    $is_feed = $this->WP_Query::is_feed;

    $this->WP_Query::init_query_flags();
    $this->WP_Query::is_404 = true;

    $this->WP_Query::is_feed = $is_feed;

    
/**
 * Fires after a 404 is triggered.
 *
 * @since 5.5.0
 *
 * @param WP_Query $query The WP_Query instance (passed by reference).
 */
    do_action_ref_array( 'set_404', array( $this ) );
  }