Modal Dialogs

        public function requestResidenceUpload(Request $request): AjaxResponse {
            $arg = $request->get('arg1');
            
            // Add an AJAX command to open a modal dialog with the form as the content.      
            $response = new AjaxResponse();
            $modal_form = $this->formBuilder->getForm('Drupal\mymodule\Form\MyForm', $arg);
            $response->addCommand(new OpenModalDialogCommand('Upload', $modal_form, ['width' => 600, 'height'=>600]) );
            return $response;        
        } 

use Drupal\Core\Form\FormStateInterface;
use Drupal\Core\Ajax\AjaxResponse;
use Drupal\Core\Ajax\CloseModalDialogCommand;
use Drupal\Core\Ajax\RedirectCommand;

/**
 * Implements hook_form_alter().
 */
function modal_form_example_form_node_article_form_alter(&$form, FormStateInterface $form_state, $form_id) {
  $form['actions']['submit']['#submit'][] = '_modal_form_example_ajax_submit';
  $form['actions']['submit']['#attributes']['class'][] = 'use-ajax-submit';
  // in some cases this was needed:
  // $form['#attached']['library'][] = 'core/jquery.form';
  // $form['#attached']['library'][] = 'core/drupal.ajax';
}

/**
 * Close the Modal and redirect the user to the homepage.
 *
 * @param array $form
 *   The form that will be altered.
 * @param \Drupal\Core\Form\FormStateInterface $form_state
 *   FormState Object.
 */
function _modal_form_example_ajax_submit(array $form, FormStateInterface &$form_state) {
  $response = new AjaxResponse();
  $response->addCommand(new CloseModalDialogCommand());
  $form_state->setResponse($response);
}