Packing slip is used for shipping.
Includign virtual product prevent companies to use the packing-slip in the correct way: Shipping with package number / descriptions.
It doesn’t make sense that packing slip include VIRTUAL product as Virtual product are by definition product that are not Shipped
https://docs.woocommerce.com/document/managing-products/
“Virtual – one that doesn’t require shipping. For example, a service. Enabling this, disables all shipping related fields such as shipping dimensions. A virtual product will also not trigger the shipping calculator in cart and checkout.”
May i suggest to include an option in WCMp setting “do not include viryual products in packing slip” ?