add_filter( 'woocommerce_related_products', 'related_products_by_attribute_improved', 10, 3 );

function related_products_by_attribute_improved( $related_posts, $product_id, $args ) {

    $taxonomy = 'brands'; // Replace with your actual product attribute taxonomy

    $term_slugs = wp_get_post_terms( $product_id, $taxonomy, ['fields' => 'slugs'] );

    if ( empty($term_slugs) ) {
        return $related_posts;
    }

    $posts_args = array(
        'post_type'        => 'product',
        'ignore_sticky_posts' => 1,
        'posts_per_page'   => 12,
        'post__not_in'       => array( $product_id ),
        'tax_query'        => array(
            array(
                'taxonomy' => $taxonomy,
                'field'    => 'slug',
                'terms'    => $term_slugs,
            ),
        ),
        'meta_query' => array(
            array(
                'key'   => '_stock_status',
                'value' => 'instock',
                'compare' => '=',
            ),
        ),
        'orderby' => 'rand',
        'fields' => 'ids',
    );

    $posts_ids = get_posts( $posts_args );

    return count($posts_ids) > 0 ? $posts_ids : $related_posts;
}