How do I hide my toolbar in SwiftUI when full screened?

I have a SwiftUI app with a toolbar with multiple WindowGroups. I want all of my windows except the main one to have a toolbar with behaviour similar to the Preview app, hiding/collapsing the toolbar when it is fullscreen.

I have .presentedWindowToolbarStyle(.unified) attached to my views and .windowStyle(.titleBar) attached to my WindowGroups.

I have tried searching for methods, asked ChatGPT multiple times and I have tried to find open-source SwiftUI apps with a collapsing toolbar but they all did not work because they were either about iOS or about an AppKit app. In code, I have tried different settings of .windowStyle and .presentedWindowToolbarStyle as well as setting .windowToolbarStyle.

I managed to achieve this by doing the following:

• First get a reference to the underlying window
• Set the window's deleate to a custom delegate which implements willUseFullScreenPresentationOptions

For the first step, you can create a NSViewRepresentable like so:

struct HostingWindowFinder: NSViewRepresentable {
    var callback: (NSWindow?) -> ()
    
    func makeNSView(context: Self.Context) -> NSView {
        let view = NSView()
        DispatchQueue.main.async { self.callback(view.window) }
        return view
    }
    
    func updateNSView(_ nsView: NSView, context: Context) {
        DispatchQueue.main.async { self.callback(nsView.window) }
    }
}

Now create the custom delegate like this:

class CustomWindowDelegate: NSObject, NSWindowDelegate {
    override init() {
        super.init()
    }
    
    func window(_ window: NSWindow, willUseFullScreenPresentationOptions proposedOptions: NSApplication.PresentationOptions = []) -> NSApplication.PresentationOptions {
        return [.autoHideToolbar, .autoHideMenuBar, .fullScreen]
    }
}

Finally, in your view, do this to set the window delegate:

struct ContentView: View {
    private var customWindowDelegate = CustomWindowDelegate()
    
    var body: some View {
        Text("Hello World")
            .background {
                HostingWindowFinder { window in
                    guard let window else { return }
                    window.delegate = self.customWindowDelegate
                }
            }
    }
}

And now whenever your ContentView goes fullscreen, it will auto hide the toolbar which can be revealed by moving your cursor to the top.