Is it possible? I choose the option "pressure" for size of the brush but nothing happens... (i am not interested in "upgrade" answers as i am on a small ressources PC).
The problem is Windows. And the Wacom driver.
Try and turn off Windows Ink.
Windows Ink is turned off, so this is an issue with all AI versions?
Ugh. You may not like this answer. In order for a Wacom tablet to have pressure sensitivity functions when connected to a Windows PC you have to enable Windows Ink in the Wacom Tablet Properties dialog box (under the "Mapping" tab in the lower left corner turn on the check box for "Use Windows Ink"). With the box checked you'll get pressure sensitivity from your Wacom tablet. But you'll also experience some other baggage that goes with Windows Ink being enabled (if you're not already familiar with the drawbacks).
One of these Windows Ink-related aggravations is a dialog box for entering hand-written text. If you click the pen tip into any text entry field, be it the address bar in a web browser, a forum reply box or even a string of point text in Adobe Illustrator you're bound to have that pop-up dialog box jump in the way of your work. Windows Ink is not smart software. It does not care if your computer has a physical keyboard boasting Cherry-MX switches and progammable RGB LED keys. It wants you to write everything by hand as if you're using a Samsung Note 5 phone. There are other behaviors involving how strings of text can be selected that just drive me bananas very quickly.
Here's an even bigger aggravation: with Windows Ink enabled if you click the pen tip and drag you'll see some odd circle icon thing pop up where the pen tip was clicked and then nothing happens. The "feature" is supposed to double as a right-click function. It's not easy to disable. Being able to press the pen tip down and drag is a pretty important function. Animated zoom relies on it. The various slider buttons in the user interface rely on click-drag functions, such as the Color palette and the sliders for each CMYK color. That circle icon thing disrupts these basic operations.
The drawbacks of Windows Ink being enabled are bad enough that I have all but given up on having any pressure sensitive functions from my Intuos Pro M tablet. I just keep the "Use Windows Ink" box not-checked about 99.9% of the time. If I want pressure sensitivity effects in a graphics device I have to rely on my iPad Pro and Apple Pencil for that. It's not the same as a full blown computer, but at least the pressure sensitivity feature works without making me want to pull my hair out. The iPad has a hand-writing text entry feature, but it's something that is easy to turn on or off (and it is off by default). I use the on-screen keyboard most of the time.
P.S., avoid using the current Wacom tablet driver for Windows (if you haven't rolled back already). The last two Wacom driver updates in January are not stable. The one from November 2022 is the latest one that doesn't cause Illustrator to crash.