taxonomy_term entity loadByProperties depth not found

The terms returned contain depth as a Term object attribute.

$vocabulary = 'category';
$entity_manager = Drupal::entityTypeManager();
$entity_storage = $entity_manager->getStorage('taxonomy_term');
$terms = $entity_storage->loadTree($vocabulary);

However, when I try to load terms by depth, I get an error.

$entity_manager = Drupal::entityTypeManager();
$entity_storage = $entity_manager->getStorage('taxonomy_term');
$terms = $entity_storage->loadByProperties([
  'vid' => $vocabulary,
  'depth' => 0,
]);

The error is the following.

Uncaught PHP Exception DrupalCoreEntityQueryQueryException: "’depth’ not found

What is the way to find attributes I can use on loadByProperties()?

  $entity_manager = Drupal::entityTypeManager();
  $entity_storage = $entity_manager->getStorage('taxonomy_term');
  $term = $entity_storage->load(1);
  kint($term);