Welcome to the forum!
Inkscape can only provide pressure sensitivity with the use of a graphics tablet (e.g. Wacom, et al.). It won't work on the canvas/ui, without that hardware.
If you are using such a tablet, and you have all the options set properly, we could file a bug report. The developers have historically kept Inkscape compatible with that kind of technology, so there's a good chance they can get it working on your tablet, before too long.
One known issue that we hear about once in a while, is if you have the computer mouse sitting on top of the tablet, it doesn't work properly.
If you use a tablet, a graphics tablet (not a tablet such as an iPad) what kind it is?
Although to be honest, I'm not sure about these touch screens. Is that what you mean?