I use a cheap smaller brand drawing tablet, and it works nearly fine in Gnome (aside from the pressure), but it isn't usable in KDE. The reason for this is that KDE moves the cursor based on the movement of the pen, not the position, and then it snaps to the position when I click the pen down. This is only a problem with the Y axis, and I can fix it by changing the
Device Accel Constant Deceleration from 1 to 1.666666, but this recreates the problem on the X axis. The reason the
Coordinate Transformation Matrix doesn't work is that it changes the coordinates of the tablet itself, not just the speed, meaning that the problem still persists, and my tablet area has been scaled down.
This is specifically a problem in the KDE Neon distribution. I tried several different distributions, even some with up to date KDE Plasma such as Kubuntu, and had no problems. I wasn't able to track down if there was a specific package in KDE Neon causing this. I've moved onto Kubuntu as a workaround now since it works, but can't provide a fix.