Im doing a promotion that if custom buy 20 or more items from catalog 102(and custom can buy anything from whole webstore), they will get 20% off. It is easy to do in cart price rule like below:

But here is the problem, if i do like this the whole cart will apply 20% off discount and this is unacceptable. And if i do in actions like below:

The cart price rule will apply to individual item but it miss the “mixed 20 or more” part.

At last i give an example: Product A, B, C in catalog 102. If custom buy 20 or more of them in any combinations they will get discount and at the same time they can buy other items in same cart without discount. Any idea how to do this? THX btw magento version is 2.17