add_action('woocommerce_after_single_product_summary', 'add_youtube_video_to_all_products', 20);

function add_youtube_video_to_all_products() {
    $youtube_video_url = 'https://www.youtube.com/embed/UDVtMYqUAyw?si=hEh8FSn46NKxdfHW';


    $youtube_video_iframe = '<iframe width="560" height="315" src="' . $youtube_video_url . '" frameborder="0" allow="accelerometer; autoplay; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>';

    echo '<div class="youtube">' . $youtube_video_iframe . '</div>';
}