ViewsTestCheckboxesThemeHooks.php

<?php

declare (strict_types=1);
namespace Drupal\views_test_checkboxes_theme\Hook;

use Drupal\Core\Form\FormStateInterface;
use Drupal\Core\Hook\Attribute\Hook;

/**
 * Form alter hooks for views tests.
 */
class ViewsTestCheckboxesThemeHooks {
  
  /**
   * Implements hook_form_FORM_ID_alter().
   */
  public function formViewsExposedFormAlter(&$form, FormStateInterface $form_state) : void {
    if (isset($form['type'])) {
      $form['type']['#type'] = 'checkboxes';
    }
    if (isset($form['tid'])) {
      $form['tid']['#type'] = 'checkboxes';
    }
  }

}