get_the_title() 返回帖子（产品）标题，包括URL中不允许的所有HTML、空格和符号等。请改用post slug。

此外，您不需要使用任何操作。

function custom_hero_image( $post_id ) {

    $product = get_post( $post_id ); 
    $slug    = $product->post_name;

    if ( is_product( $post_id ) ) {
        $html = \'<img class="jarallax-img" src="\'. get_template_directory_uri() .\'/inc/assets/img/shop/hero/\'.$slug.\'.jpg">\';
    } else {
        $html = \'<p>No results found.</p>\';
    }
    return $html;
}

<div id="hero">
    <?php
        // get the post ID outside the Loop
        $post_id = get_queried_object_id();
        // print the <img>
        echo custom_hero_image( $post_id );
    ?>
</div>