For those on Windows PC, In Illustrator go to Preferences/Devices Click the "Enable Wacom" box. That's all I needed to do. I would have saved myself a couple of hours if someone had mentioned that here. You might have to do the Preferences/Plugin-in & Scratch Disks and click Additional Plugin-ins Folder and choose your Wacom folder, in my case C:\Program Files\Tablet\WaCom\.... then restart Illustrator? I had done those steps earlier, but it was the Devices... "Enable Wacom" step that finally solved the grayed out brush options problem.

This worked for me, I couldn't see or add Illustrator in my Automation setting before:

Ok, solved my problem. I had to install an older version of Illustrator (v25.0). When I did that, it prompted an agreement to control the tablet from Illustrator, which hadn't been prompted in the latest version of Illustrator. When I accepted this agreement, Illustrator appeared in the Automation menu and started working with the pen pressure.

https://www.reddit.com/r/MacOS/comments/obmu9g/adding_adobe_illustrator_to_the_security_privacy/

This is for people for whom NONE of this helps (and no other help from any other forum for the past year)

1. Find a file from happier times, where pressure brushes were used.
2. Copy the objects into you current file
3. The brushes used in the objects you just pasted in, should appear in your brush pallette - the pressure option is active in these brushes!!
4. Adjust these brushes to your current need and use them freely

Sometimes this causes my Illustrator to crash. Other times not. Still,

5. Ask for your money back

Thanks KB that worked for me!!

OMG, finally I figured it out with the help of so much research.
Simply add the "Wacom Desktop Center" to "Accessibility" in System Preference. Along with making sure Illustrator is added in as well.

searching for the answer while using an xp pen duos 2 tablet on a Mac running Catalina...this suggestion worked for me:
from within illustrator,
As suggested I went to Preferences > Plug-Ins & Scratch Discs, ticked additional plug-ins folder
then found the xp tablet and pressed select folder
The folder that worked for me was in "Applications/pentablet"
I also thought it would be more specific, but that worked fine.
I restarted illustrator and got the option for Pressure, SUCCESS
I had trouble overall installing the driver as there actually wasn't one on the xp pen site that supposedly has all that you need. I ended up installing the driver from the duos pro and with some fix its here and there got it to work.

Hi! I just saw this solution in a youtube comment section but command+shift+alt worked for me. hope this helps

Thanks Karolina!!!!! This issue was really a headache!!!! Can´t believe I could finally solve it! Thanks again!!!! :)

The same thing happened on Ai on my desktop. Any suggestions?

Thanks @TomG!!!!!!!!!!!!!! Finally

Thanks, @TomG and @Ribeye Designs this worked for me too!
As suggested I went to Preferences > Plug-Ins & Scratch Discs, ticked additional plug-ins folder
then found the Wacom folder and pressed select folder
The folder that worked for me was in "Applications/WacomTablet"
I also thought it would be more specific, but that worked fine.
I restarted illustrator and got the option for Pressure, SUCCESS!

I had the same problem but now it’s been solved.

Thank you Tenacious Game's! And thank you my anonymous friend for translation!

Thanks @TomG that worked for me
As suggested I went to Edit > Preferences > Plug Ins & Scratch Discs, ticked additional plug-ins folder
then found the wacom folder and pressed select folder
The folder that worked for me was in "C:\Program Files\Tablet\Wacom"
I thought it was going on be more specific than that but that worked fine, once I chose that folder, then restarted illustrator (not sure this was even necessary) I got the option for Pressure

sorry, but im facing the same problem and i cant find the steps, im new to illustrator and the pressure option is greyed out please help?

Thanks Karolina I followed the steps and now I'm up and running :)

it is a generic problem

I'm having the same issue

I have tried all of the answers listed and still these options are greyed out :(

***** all the "real candidates".... Tenaciousgames saved my day and I'm nominating him for President in 2020!!! (and Karolina for VP)

Tenaciousgames saved the day!