[dsr_]

In X11 (and probably in Wayland, since this is a libinput thing) you can define a button as a scroll lock.

So, hold down the scroll lock button and the thumbstick becomes a scroller. That leaves three buttons for left, middle and right.

[pronik]

Sure, but which of those buttons would be suitable? Keep in mind, it will be your thumb that needs to land naturally on that button while your index finger rests on the trackpoint. And the scroll button is also usually the middle button even though there are cases where you need middle-mouse drag (looking at you, Blender) for which a fourth button might go quite nice.

[dsr_]

I'm right handed, so I would pick the bottom left button as the scroll lock, with the top left button as 1, top right button as 2, and bottom right as 3.

"scroll button is also usually the middle button" -- these functions are completely separable in libinput.

[pronik]

Meaning you would be pressing LMB and RMB with your index finger, moving it from the trackpoint itself? I can imagine controlling the trackpoint with the middle finger and use the index and ring finger to press the buttons, but it's far away from the "original" way to do it.