I use linux with a laptop. I can use a touchscreen pen at the touchpad and I can paint with it in Krita.
The problem is I can't use the pressure sensitivity of the laptop touchpad with the brushes of Krita.
The test program "evtest" shows that the touchpad sends values for the pressure but Krita doesn't get them.
Krita should treat the touchpad device as a digitizer device, not as a mouse.

I've never heard of a laptop with a pressure sensitive touchpad, so maybe the very first thing you should have shared with us is the brand, make and model of your laptop?