Steps to reproduce:

1. Open Qt Creator and start a new QtQuick 2 project and don't change anything at all.
2. Build the project for android devices.
3. Start an android emulation with resolution 800x2000
4. Deploy the apk to the emulation and run it
5. See the blank space at the bottom of screen (it's transparent and shows what's behind the app.)

If you have a Galaxy Note 8 device you don't need the emulation.

It happens on all devices with long screens running Oreo.

    qWarning() << QApplication::screens().at(0)->size();
    qWarning() << QApplication::screens().at(0)->availableSize();

in main.cpp and

    onWidthChanged: console.log('width: ' + width)
    onHeightChanged: console.log('height: ' + height)

in main.qml both show wrong values (regardless of the dpi of the device the aspect ratio of the values printed does not match 800x2000.)

The problem does not occur in Android 7.

Related stackoverflow post:

https://stackoverflow.com/questions/51078344/app-leave-blank-space-in-bottom

Notice that in this post the developer has changed the them in the manifest, but it happens without any change to the default manifest provided by Qt Creator.

Also notice that this post is not related to Qt so seems like something has changed in Android 8.