You can make an app go fullscreen (hide status bar and/or immersive mode on Android 4.4) by setting the QQuickView's windowState to Qt::WindowFullScreen.

To exit fullscreen mode, setting it back to Qt::WindowNoState does not work, you need to use Qt::WindowMaximized instead.

The issue lies in qtbase/src/plugins/platforms/android/qandroidplatformwindow.cpp in updateStatusBarVisibility() where it only calls QtAndroid::showStatusBar() on Qt::WindowMaximized but not on Qt::WindowNoState.