Changing 2 Elements on Ajax Callback
Instead of returning a single render array (of all or part of your form) from your callback, you will need to return an AjaxResponse that contains a  ReplaceCommand for each piece of the form you want to replace:
For example, in your callback:
$response = new AjaxResponse();
$response
  -&gt;addCommand(new ReplaceCommand('#edit-form-factor', $form_factor_element))
  -&gt;addCommand(new ReplaceCommand('#edit-model', $model_element));
return $response;

See the guide:
https://www.drupal.org/docs/drupal-apis/ajax-api/basic-concepts#sub_form
And the Ajax commands reference:
https://www.drupal.org/docs/drupal-apis/ajax-api/core-ajax-callback-commands