drupal 8 custom form entity reference views
Converting a custom form element in Drupal 8 to using an entity reference view is an annoyingly simple thing to do once you have the custom code to perform the task. Unfortunately, it's not terribly well documented on the internet and thus searching without the right combination of words won't yield results, hence I'm writing this with an entirely different description than is in the linked article. Anyways, here is how you do Drupal 8 custom form element for entity reference views.
$form['entity_id']['widget']['target_id']['#selection_handler'] = 'views'; $form['entity_id']['widget']['target_id']['#selection_settings'] = [ 'view' => [ 'view_name' => 'VIEW_MACHINE_NAME_HERE', 'display_name' => 'entity_reference_1', 'arguments' => , ], ];