Add SKU in Product Title

In the above code. You are adding the SKU code on all the product on every post saved. Instead of all post you should just update only product which you are updating. And send you should check if SKU already added then no need to add it again.

// Call this function each time a product updated
function woo_product_append_sku_to_titles( $product_id ) {
    
    $_product = wc_get_product( $product_id );

    $_sku = $_product->get_sku();
    $_title = $_product->get_title();

    $sku_find = strpos( $_title, $_sku );

    if( $sku_find === false ) {

        $_new_title = $_sku . "-" . $_title;

        global $wpdb;
        
        $where = array( 'ID' => $product_id );
        $wpdb->update( $wpdb->posts, array( 'post_title' => $_new_title ), $where );
    }
}
add_action( 'save_post_product', 'woo_product_append_sku_to_titles', 20, 2 );

Once you update or create any product, the SKU will be added in that post. And if already added then it will not add.