When using evdev, QT can rotate the touch input to match a rotated screen via the QT_QPA_EVDEV_TOUCHSCREEN_PARAMETERS variable. However, if you are using libinput, there is no such method.

It's noted in QTBUG-53768 that this is the case, but the resolution there is that wayland should  support this functionality, not Qt. But if you are using eglfs, rather than wayland (eg, on a raspberry pi) this doesn't solve the issue.

We have implemented a patch that does this, attached. We just did this by passing the libinput coordinate transform matrix as an environment variable, but I guess you might want it to be compatible with the arguments used in QT_QPA_EVDEV_TOUCHSCREEN_PARAMETERS. It's probably worth our while to do that rather than building a patched version, so we could make a version which uses the same args if you want.