Ajax callback inside views plugin doesn't work.

Changes are made on on 11.x (our main development branch) first, and are then back ported as needed according to our policies.

I can confirm this issue when placing the ajax callback within the same class that provides the options form

however a simple fix would be placing the ajax callback on your .module file
something like this

/**
   * {@inheritdoc}
   */
  public function buildOptionsForm(&$form, FormStateInterface $form_state) {
    parent::buildOptionsForm($original_form, $form_state);
    $form['test']=[
      "#type" => "select",
      '#default_value' => "test",
      "#title" => t("Component"),
      "#options" => ['test'=>'test','test2'],
      '#ajax' => [
        'callback' => '_your_module_ajax_callback',
        'wrapper' => 'test',
        'effect' => 'fade',
        '#suffix' => '<div id="test"></div>'
      ],
      '#executes_submit_callback' => FALSE,
      '#required' => TRUE,
    ];
  }

and in your .module file

function _your_module_ajax_callback($form,FormStateInterface $form_state ) {
    return ['#markup'=>'hello'];
  }