Qt WebEngine: PDF viewer cannot be scrolled by touch in fullscreen mode

Steps to reproduce

1. Prepare a machine with a touchscreen
2. Build and run the WebEngine Quick Nano Browser example (https://doc.qt.io/qt-6/qtwebengine-webenginequick-quicknanobrowser-example.html )
3. Enter this URL and wait for it to finish loading: https://www.learningcontainer.com/wp-content/uploads/2019/09/sample-pdf-download-10-mb.pdf
4. Use the touchscreen to swipe/scroll the PDF document
5. Tap the "More Actions" menu (3 dots on the top-right) and select "Present" to enter fullscreen mode
6. Use the touchscreen to swipe/scroll the PDF document

Outcomes

1. (Step #4) The document can be scrolled by touch (Expected)
2. (Step #6) The document no longer scrolls by touch (Not Expected)