Hi,
In each product, when you edit it, you have a "quantity input" setting. This setting allows you to decide how to display the quantity input or even hide it for that specific product. So you could just set it to "none" for digital products.
And if you want to make it automatic based on the weight of the product (when the weight is 0, the product is considered a virtual good and no shipping is required unless the "force shipping regardless of weight" setting is activated in the HikaShop configuration), you can create two mass actions with a trigger "after a product is updated" and a filter on the product_weight with an action "update the values" on the column product_quantity_layout to set the value automatically.