Add Custom element item in wp nav menu

Last item for wp_nav_menu

function add_last_nav_item( $items ) {
    $items .= sprintf(
        '<li class="nav__item social__icon">
   <figure class="icon__container">
     <div class="icon">
      <a href="51$s" target="_blank" class="social__link"><img src="%2$s/images/icon__facebook.svg"></a>
     </div>
     <div class="icon">
       <a href="%3$s" target="_blank" class="social__link"><img src="%2$s/images/icon__youtube.svg"></a> .
     </div>
   </figure>
  </li>',
        'https://www.facebook.com/Czysta-%C5%9Awiadomo%C5%9B%C4%87-%C5%9Awiat%C5%82o-i-Mi%C5%82o%C5%9B%C4%87pl-811435542275919/',
        get_template_directory_uri(),
        'https://www.youtube.com/channel/UCxxKwAW7JE6eCx3OjNcO6Yw/'
    );

    return $items;
}

add_filter( 'wp_nav_menu_items', 'add_last_nav_item' );