Click the 
icon for any virtual option.
If you click the checkbox for Multiselect it will allow the customer to choose multiple variants.
You can choose between the following options:
- no restriction
- must choose at least
- must choose at most
- must choose exactly
Once the customer clicks the add to cart button an alert will pop up if conditions aren’t met.
This option isn’t compatible with our Shopify Options
Demo: https://variantcustomproductoptions.com/collections/examples/products/pick-and-mix-gift-box