I created a new Catalog Price Rule on my Magento CE 2.3.2
I also have in my products 2 custom attributes: brand and season.
I have 3 products:
How I created the rule:
Websites=All selectedCustomer Groups=All selectedFrom Date=Today datePriority=0
If [ALL] of these conditions are [TRUE]:
Brand [IS] X (selected from dropdown list)
Season [IS] Y (selected from dropdown list)
Category [IS NOT/NOT CONTAINS/IS NOT ONE OF] 5 (I tried with this 3 options)
Apply=first option selected
I tried with a lot of combination but there is no way to exclude a product of a specific category.
Hope for help, thanks in advance.