How to show view below title bar for macOS in SwiftUi

[onmyway133]

Use NSTitlebarAccessoryViewController

var titleBarAccessoryVC: NSTitlebarAccessoryViewController {
    let vc = NSTitlebarAccessoryViewController()
    let view = HStack {
        Spacer()
        Button {
            
        } label: {
            Text("Save")
        }
        .buttonStyle(.borderedProminent)
        .controlSize(.large)
    }
    .padding(.horizontal)
    
    vc.view = NSHostingView(rootView: view)
    return vc
}

let window: NSWindow = ...
window.addTitlebarAccessoryViewController(titleBarAccessoryVC)