Thank you! yes of course, it was greyed out because I was not in custom mode. I was wondering if it was because I am actually using BCN3D Cura SW version 2.0.0. And since I am on this topic, why is there a special BCN3D Cura version for the BCN3D printers like sigma or sigmax, instead of having the same Cura version 3.2.1 handle that printer among all the others?
Anyway I will experiment now with manual support, as I can't make any sense of what the Sigma printer produces when I select "add Support" using BCN3D Cura.