Hi,
I think you might be better off creating a custom macro method and using that to carry out your logic. Kentico 12 documentation provides a good example using product categories, see here.
Use the macro you create on it's own in the Further conditions field, and leave the Minimum order amount field empty. You can then pass the name of the product category and order subtotal into the macro method like this:
Data.ContainsProductsInCategory("GiftCards", Subtotal)
You can loop over the basket items see if they have been assigned the gift card category, and also check the subtotal you've passed into the macro method as a parameter.