How to limit the taxonomy terms in 'Exposed Drupal Views filters', to the tags that are used in included nodes, in multiple Views

/**
 * Implements hook_form_alter()
 *
 */
function YOURMODULE_form_alter(&$form, \Drupal\Core\Form\FormStateInterface $form_state, $form_id) {
  // Id's of the forms we want to alter.
  $form_ids = [
    'views-exposed-form-resources-page-1' => 'resource',
    'views-exposed-form-reviews-page-1' => 'review',
    'views-exposed-form-available-for-review-page-1' => 'review',

  ];
  // Targeted taxonomy term fields.
  $select_fields = ['tid_2', 'field_tags_target_id'];
  // Continue only if current form_id is one in defined array.
  if (array_key_exists($form['#id'], $form_ids)) {
    // Loop through targeted fields.
    foreach ($select_fields as $select_field) {
      // Get 'terms in use', switch query on which field is currently in the loop.
      // This only works if you have 1 or 2 targeted filters.
      $available_terms = ($select_field == 'tid_2')
                        ? _get_available_terms_region($form_ids[$form['#id']], $form['#id'])
                        : _get_available_terms_tags($form_ids[$form['#id']], $form['#id']);
      // Continue if $available_terms exists.
      if (isset($available_terms)) {
        // Unset the existing list.
        unset($form[$select_field]['#options']);
        // Build new list with 'terms in use'.
        $form[$select_field]['#options']['All'] = '- Any -';
        foreach ($available_terms as $available_term) {
          $tid = $available_term[0];
          $name = $available_term[1];
          $form[$select_field]['#options'][$tid] = $name;
        }
      }
    }
  }
}

/**
 * Custom function to query and build new filter list.
 *
 * @param $node_type
 * @param $exposed_block_id
 * @return array
 */
function _get_available_terms_region($node_type, $exposed_block_id) {
  // Table name of tags field.
  $node_tags_table = 'node__field_profile_region';
  // Query data.
  $query = \Drupal::database()->select($node_tags_table, 'nft');
  $query->distinct();
  $query->join('taxonomy_term_field_data', 'tname', 'tname.tid = nft.field_profile_region_target_id');
  $query->join('node', 'node', 'node.nid = nft.entity_id');
  $query->fields('nft', ['field_profile_region_target_id']);
  $query->fields('tname', ['name']);
  $query->orderBy('tname.name');
  // Dynamically query node type.
  $query->condition('node.type', $node_type);
  if($exposed_block_id == 'views-exposed-form-available-for-review-page-1') {
    $query->join('node__field_boolean_1', 'available', 'available.entity_id = nft.entity_id');
    $query->condition('available.field_boolean_1_value', 1);
  }
  $result = $query->execute();
  // Build term list.
  $term_list = [];
  while ($row = $result->fetchAssoc()) {
    array_push($term_list, [$row['field_profile_region_target_id'], $row['name']]);
  }
  // Return term list.
  return $term_list;
}

/**
 * Custom function to query and build new filter list.
 *
 * @param $node_type
 * @param $exposed_block_id
 * @return array
 */
function _get_available_terms_tags($node_type, $exposed_block_id) {
  // Table name of tags field
  $node_tags_table = 'node__field_tags';
  // Query data.
  $query = \Drupal::database()->select($node_tags_table, 'nft');
  $query->distinct();
  $query->join('taxonomy_term_field_data', 'tname', 'tname.tid = nft.field_tags_target_id');
  $query->join('node', 'node', 'node.nid = nft.entity_id');
  $query->fields('nft', ['field_tags_target_id']);
  $query->fields('tname', ['name']);
  $query->orderBy('tname.name');
  // Dynamically query node type.
  $query->condition('node.type', $node_type);
  if($exposed_block_id == 'views-exposed-form-available-for-review-page-1') {
    $query->join('node__field_boolean_1', 'available', 'available.entity_id = nft.entity_id');
    $query->condition('available.field_boolean_1_value', 1);
  }
  $result = $query->execute();
  // Build term list.
  $term_list = [];
  while ($row = $result->fetchAssoc()) {
    array_push($term_list, [$row['field_tags_target_id'], $row['name']]);
  }
  // Return list.
  return $term_list;
}