How to use a transparent window as the desktop background?

[senmx]

In macOS, if you use objective-c, you can probably achieve it like this:

- (void)setupWindow {
    NSWindowStyleMask mask = NSWindowStyleMaskBorderless |
                             NSWindowStyleMaskResizable |
                             NSWindowStyleMaskFullScreen;
    
    self.window.styleMask = mask;
    self.window.level = kCGDesktopWindowLevel;
    self.view.wantsLayer = YES;
    self.view.layer.backgroundColor = [NSColor clearColor].CGColor;
    self.window.backgroundColor = [NSColor clearColor]; 
}

And how to do it with QT?
Get the top-level window QWindow and then convert it to NSWindow, and then use objective-c to implement it?