Display status message after submitting modal popup form
After redirection the \Drupal::messenger() may not work. So try with the Drupal OpenModalDialogCommand
use Drupal\Core\Ajax\OpenModalDialogCommand;

/**
* {@inheritdoc}
*/
  public function submitForm(array &amp;$form, FormStateInterface $form_state){
    
    $entry_entity = \Drupal::entityTypeManager()-&gt;getStorage('entry')-&gt;load($entry_id);
    $entry_entity-&gt;delete();

    $response = new AjaxResponse();
    $response-&gt;addCommand(new OpenModalDialogCommand(&quot;Success&quot;, 'Entity deleted.', ['width' =&gt; 800]));
    return $response;
  }