How can I load a Store by user ID?
The user ID is saved on the store when it's created. Therefore you can load it with code similar to the following one.

$store = \Drupal::entityTypeManager()-&gt;getStorage('commerce_store')-&gt;loadByProperties(['uid' =&gt; \Drupal::currentUser()-&gt;id()]);


That will load the store based on the currently logged-in user.