On Android pressing the back button is handeled in QGuiApplicationPrivate::processKeyEvent and leads to a call of ApplicationWindow::onClosing where we can decide to accept the close or only go back and reject the close. iOS has no back button but VoiceOver provides a Z gesture to go back. So we should handle this in the same way as for Android. This would allow to use the same Code for both platforms:

ApplicationWindow {
	onClosing: pClose => {
		if (mainPage && Qt.platform.os === "android") {
			pClose.accepted = true;
			return;
		}

		pClose.accepted = false;
		executeBackAction();

	}
}