How to allow html tag in menu?
Following solution works:

use Drupal\Core\Render\Markup;

/**
 * Implements hook_preprocess_HOOK()
 */
function YOURTHEME_preprocess_menu(&amp;$variables){
  foreach($variables['items'] as &amp;$link){
    $link['title'] = Markup::create($link['title']);
  }
}


Source: Allow html into menu item names - Solution for Drupal 8