Display product (variation) description in a new line on WooCommerce order received page and emails

Solution:

To display the $decription on a new line, you can use the woocommerce_order_item_meta_start action hook versus woocommerce_order_item_name filter hook.

So you get:

function action_woocommerce_order_item_meta_start( $item_id, $item, $order, $plain_text ) {
    // Get product
    $product = $item->get_product();

    // Variation description
    if ( $item['variation_id'] > 0 ) {
        $description = $product->get_description();
    } else {
        // Product short description (for others)
        $description = $product->get_short_description();
    }
    
    echo '<div>' . $description . '</div>';
}
add_action( 'woocommerce_order_item_meta_start', 'action_woocommerce_order_item_meta_start', 10, 4 );