field_field_storage_config_update

field_field_storage_config_update(FieldStorageConfigInterface $field_storage)

function field_field_storage_config_update(FieldStorageConfigInterface $field_storage) {
  if ($field_storage->isSyncing()) {
    // Don't change anything during a configuration sync.
    return;
  }

  // Act on all sub-types of the entity_reference field type.
  /** @var \Drupal\Core\Field\FieldTypePluginManager $field_type_manager */
  $field_type_manager = \Drupal::service('plugin.manager.field.field_type');
  $item_class = 'Drupal\Core\Field\Plugin\Field\FieldType\EntityReferenceItem';
  $class = $field_type_manager->getPluginClass($field_storage->getType());
  if ($class !== $item_class && !is_subclass_of($class, $item_class)) {
    return;
  }

  // If target_type changed, reset the handler in the fields using that storage.
  if ($field_storage->getSetting('target_type') !== $field_storage->original->getSetting('target_type')) {
    foreach ($field_storage->getBundles() as $bundle) {
      $field = FieldConfig::loadByName($field_storage->getTargetEntityTypeId(), $bundle, $field_storage->getName());
      // Reset the handler settings. This triggers field_field_config_presave(),
      // which will take care of reassigning the handler to the correct
      // derivative for the new target_type.
      $field->setSetting('handler_settings', []);
      $field->save();
    }
  }
}