For Testing: Delete most nodes, leave a limited, randomly sorted of each content type.

deleteBulkNodes.install

/**
 * Implements hook_update_N().
 *
 * Remove nodes for faster testing.
 */
function hook_update_8001(&$sandbox) {
  $etm = \Drupal::entityTypeManager();
  $types = $etm->getStorage('node_type')->loadMultiple();
  $nodeStorage = $etm->getStorage('node');
  foreach ($types as $label => $type) {
    $ids = $etm->getStorage('node')->getQuery()
      ->condition('type', $label)
      ->execute();
    shuffle($ids);
    $keep = array_slice($ids, 0, 25);
    $remove = array_diff($ids, $keep);
    foreach($remove as $id) {
      $node = $nodeStorage->load($id);
      if ($nodeStorage->delete([$node])) {
        \Drupal::messenger()->addMessage((int) $id . ' Deleted');
      }
    }
  }
}