I implemented it by using a Popup control with two states expanded and collapsed and changing the modal property so that when is collapsed it is not modal and when is expanded is modal. Also I added a transition animation.

The only thing I am missing is the "drag" feature...I am sure it can be done but is a bit more complex and probably I will not need this feature.

@jpnurmi
Well, I found a temporary solution while the original idea is fixed with dragMargin. Making the width is 0 can disable the Drawer, but only with the combination of width and dragMargin, if only use width, is still possible show a Drawer (an empty drawer)

Drawer { dragMargin: appContentManager.depth > 1 ? 0 : Qt.styleHints.startDragDistance width: appContentManager.depth > 1 ? 0 : Math.min(appRoot.width, appRoot.height) / 3 * 2 }

I also report the bug
https://bugreports.qt.io/browse/QTBUG-54629