When the option "Hide statusbar during launch" in XCode is enabled, the status bar is not shown in the app after launch. You can either disabled the option, which means, the status bar is also drawn ontop of your splash screen, or the status bar will not be visible at all.

Using an QML ApplicationWindow as root item inside a QQmlEngine (not using QQuickView - which always reserves space for the status bar and you cannot ever draw behind it), I ran qmake and opened the resulting project in XCode and enabled the "Hide during application launch" option in the project's General settings.