Hi Alain,
I’m on iMac OS Mojave, if this helps. Even up to now the pen pressure doesn’t work whenever I open AP, but by doing either “Add blank drawing” (Command + Arrow Down) or “Insert blank drawing” (Cmd + Arrow Up) makes the pen pressure to work. I’ve been getting used with this that before I start working, I draw a line first just to see the pen pressure (not working), so I’d delete that drawing, and just do this ‘technique’ (Add/Insert blank drawing for now), so that I don’t need to draw a lot just to make the pen pressure work.
As for the Wacom pen settings, if this helps also. I didn’t change anything specifically for AP, just the default setting.
Hope there’s another way that will work for you too.