Including dolphin, plasma desktop, konsole... but only on Wayland, also gtk3 apps are not affected. Also there is a region on the screen that doesn't do this. Since Qt 5.14 Beta1
Same thing here after update to Qt 5.14 beta1. And kwin_wayland causes high cpu usage while cursor is positioned on Qt apps running natively on Wayland. High cpu usage stops if cursor is positioned on Xwayland apps.
It's still there with plasma 5.17.0 For some reason it stops flashing/flickering in when i hover along the title-bar in qt-windows. Just out of the blue I tried setting the dpi-size of the the cursor to a fixed size but that also does not fix the problem.
*** This bug has been marked as a duplicate of bug 412924 ***