Get a field instance's settings
Using the entity_field.manager service, you are able to get an array of BaseFieldDefinition classes. This service is injectable as well, but for copy-paste working code, you can do the following:

$bundle_fields = \Drupal::getContainer()-&gt;get('entity_field.manager')-&gt;getFieldDefinitions($entity_type, $bundle);
$field_definition = $bundle_fields[$field_name];
$catalog_id = $field_definition-&gt;getSetting($setting_name);