Touch input is totally broken or behaves very strangely with a Wacom touchscreen on X11 when using the wacom driver instead of the libinput driver

Since getting a Lenovo ThinkPad X1 Yoga with a 4K Wacom touchscreen, touch functionality throughout Qt software no longer works on X11 (it works on Wayland). Software written with GTK or Electron is not affected, so I am suspecting Qt.

In QtWidgets apps and QtQuick apps, tapping on the touchscreen does not generate click events. The cursor moves, and the item therefore enters its hovered state. Sometimes it also becomes visibly selected, but it has not actually been clicked. I have not been able to find a pattern for this. Sometimes it becomes visibly selected, sometimes it doesn't.

Additionally, in QtQuick apps, scrollviews and flickables do not scroll with a one-finger tap-and-drag/swipe.

Interestingly enough, tap-and-hold on the Plasma desktop wallpaper itself works flawlessly. But nothing else does.

I am willing to send any necessary logging and debug as needed. Other colleagues affected by this issue all have laptops with Wacom touchscreens, so that seems to be the common denominator.