How to load all aliases of a domain
Got it.

The 'hostname' is not a property of the alias. The way to get the aliases is:

$aliases = \Drupal::entityTypeManager()-&gt;getStorage('domain_alias')-&gt;loadByProperties(['domain_id' =&gt; 'my_domain_id']);


Note that 'my_domain_id' is specific to the domain that you are trying to get the alias for.