Generate Test Menu - Drupal 8/9

gen_menu.php

function _build_test_menu($link_title, $how_many, $full_depth = 3, $parent_id = NULL, $current_depth = 1) {
  $menu_link_storage = \Drupal::entityTypeManager()->getStorage('menu_link_content');
  for ($a = 1; $a <= $how_many; $a++) {
    $new_title = $link_title . $a;
    if ($current_depth != $full_depth) $new_title .= ".";

    $item1 = $menu_link_storage->create([
      'title' => $new_title,
      'link' => ['uri' => 'internal:/'],
      'menu_name' => 'main',
      'parent' => $parent_id,
      'expanded' => TRUE,
      'weight' => 1,
    ]);
    $item1->save();

    if ($current_depth < $full_depth) {
      _build_test_menu($new_title, $how_many, $full_depth, "menu_link_content:" . $item1->uuid(), ($current_depth + 1));
    }
  }
}

_build_test_menu("Item: ", 1, 2);