I am using Ubuntu 24 Noble. This per default goes with wayland, but since we are developing an x11-based application, reconfigured to use x11. My laptop also has a touchscreen, since we are developing touch applications.
When using x11, both QtCreator 17.0.0 and qt-applications do not respond to single-finger touch events at all. I have enabled debug-logging on all handlers and events and only receive anything when two fingers touch something in the application (recognized as a single click). Any single finger tap/click/press does not appear at all in the event logs.

The system however recognizes these events correctly. Logging the events of X11 shows that the system recognizes an event (Single finger actions work system-wide, except in qt).

Switching to wayland fixes the touch issue, but brings another set of problems on the application side.

Edit: The same thing happens with independent external touchscreens, not only with the internal laptop screen. I already have tried setting various env. variables found in forum posts to no avail.
Most of the env. variables had no effect at all, one notable exception:
qputenv("QT_XCB_NO_XI2", "0");
also disabled the two-finger interaction as single click (so nothing at all happened when tapping regardless how many fingers one used)