Hi Thanks a lot for the answer. That makes sense.
So I tested it, I could create the BOM, which I was planning to build as a kit.
I created 4 attributes (bottle 1 to 4) and then the 9 values for each of them (TypeA, TypeB...).
I filled up the BOM with Apply on Variants. E.g. TypeA ot bottle, I had apply on variants : Bottle 1:TypeA, Bottle 2:TypeA ; Bottle 3:TypeA ; Bottle 4:TypeA.
When I create the sales order, I can indeed select which option I want to see. I confirm the sale, but when I go in delivery, on the detailed Operations or in the Operations tab, I see just the box (which is in the BOM of the gift box but not assigned to any specific variant. Just for trial, when I assigned TypeA to all bottles, I could see a quantity one of TypeA in the Operations tab.
Variants have been causing me some headaches... THanks!