EntityQuery with joins
The easiest way to load a field from any entity when querying is to use the entityTypeManager:

$users = \Drupal::entityTypeManager()-&gt;getStorage("user")
        -&gt;loadByProperties(['uuid' =&gt; $uuid]); // or any other properties.

foreach ($users as $user) {
    var_dump($user-&gt;field_customfield-&gt;getValue());
}


see:  working-with-the-entity-api

Be careful to not use \Drupal::entityManager, since it is deprecated.