Unfortunately we have the same issue https://bugreports.qt.io/browse/QTBUG-44195 now, with Qt 5.9.2 on macOS 10.13.1. We use the following flags to our customised main app window: 

`Qt.FramelessWindowHint | Qt.Window | Qt.NoDropShadowWindowHint` and we can not minimise it by using

`showMinimized()` method.

Here is the original message from https://bugreports.qt.io/browse/QTBUG-44195 :

for our project, we need to fully customize the window. to achieve this, we create a frameless window and draw a fake titlebar on the frameless window.

but we found out that frameless Qt app under mac can't perform maximize and minimize.

in the attachment, you can find a simple app that reproduces the issue. there is a button on the frameless window, click that button will call showMinimize(), but the window stays.

but the same app works on windows.