monster_menus-9.0.x-dev/modules/mm_media/tests/modules/mm_media_fileref_type/mm_media_fileref_type.module

<?php

use Drupal\Core\Entity\EntityTypeInterface;
use Drupal\field\Entity\FieldConfig;

/**
 * Implements hook_entity_bundle_field_info().
 */
function mm_media_fileref_type_entity_bundle_field_info(EntityTypeInterface $entity_type, $bundle, array $base_field_definitions) {
  // Connect the field instance to the custom media type. Without this the
  // field data doesn't get saved correctly.
  if (!strncmp($bundle, 'createMediaType', 15)) {
    if ($field_instance = FieldConfig::load('media.file.field_media_file')) {
      return [$field_instance->getName() => $field_instance];
    }
  }
}