Discount on all products/categories except some c

Hi,

You can't exclude categories or products from discounts. You can only restrict discounts to categories and products.

So I would recommend to look at the mass actions system of HikaShop (menu System>Mass actions).
There, you could have a bunch of filters on the category of the products so that you filter the products which are not in these 4 categories, and then add an action to add them to a specific category that you previously created.
That way, you can then just configure a discount for that category which will encompass all products expect the ones from these 4 categories.