Create Custom Select Webform Element
After long research about Webform elements, I have finally figured out the solution. Extend the Select Element. :)
use Drupal\Core\Render\Element\Select;

class Facility extends Select {

  /**
   * {@inheritdoc}
   */
  public function getInfo() {
    $properties = parent::getInfo();
    $class = get_class($this);
    $properties['#process'][] = [$class, 'processMyCustomSelect'];

    return $properties;
  }

 public static function processMyCustomSelect(&amp;$element, FormStateInterface $form_state, &amp;$complete_form) {
    // Here you can add and manipulate your element's properties and callbacks.
    return $element;
  }
}

this post really helped me out a lot: Webform Custom Radios/Checkboxes Element does not get rendered in webform : Drupal 8