Example of cross platform Qt app (desktop, mobile)

One of value proposals of Qt is that it allows making applications for:
Linux, Mac, Windows, Android, iOS.

Here links regarding mobile:

* https://doc.qt.io/qt-5/android.html
* https://doc.qt.io/qt-5/ios.html

Could you please add example, illustrating project that can be compiled to each platform (with simple build instructions ) ?