pressure sensitivity option greyed out on adobe illustrator 2019

[#1]

I have recently bought a Wacom Intuos pro to use with the illustrator app, but I can't get the pressure sensitivity to work. pressure is greyed out when I go to brush options under size. I use a Macbook Air, OS Catalina 10.15.2. and I followed all Wacom installation instructions originally.

[#2]

I have recently bought a Wacom Intuos pro to use with the illustrator app, but I can't get the pressure sensitivity to work. pressure is greyed out when I go to brush options under size. I use a Macbook Air, OS Catalina 10.15.2. and I followed all Wacom installation instructions originally.

[#3]

In the Illustrator preferences there is a Wacom setting. It can be on or off. There also is a "Live preview" (in "Performance") option which can be on or off.

Can you please try with different combinations of those 2 options?

And then also try the Wacom 6D brushes library. Do any of those work?