OK got it! First start the Xcode project with LifeCycle -> AppKit App Delegate, not SwiftUI App. In the AppDelegate.swift file add:     let mainScreen: NSScreen = NSScreen.screens[0]     window.contentView?.enterFullScreenMode(mainScreen) at the end of func applicationDidFinishLaunching. Looks like this: class AppDelegate: NSObject, NSApplicationDelegate {   var window: NSWindow!   func applicationDidFinishLaunching(_ aNotification: Notification)   {     // Create the SwiftUI view that provides the window contents.     let contentView = ContentView()     // Create the window and set the content view.     window = NSWindow(         contentRect: NSRect(x: 0, y: 0, width: 480, height: 300),         styleMask: [.titled, .closable, .miniaturizable, .resizable, .fullSizeContentView],         backing: .buffered, defer: false)     window.makeKeyAndOrderFront(self)     window.isReleasedWhenClosed = false     window.center()     window.setFrameAutosaveName("Main Window")     window.contentView = NSHostingView(rootView: contentView)// start App in fullScreen mode     let mainScreen: NSScreen = NSScreen.screens[0]     window.contentView?.enterFullScreenMode(mainScreen)   }   func applicationWillTerminate(_ aNotification: Notification)   {     // Insert code here to tear down your application   } } And finally set the background color of contentView to white, otherwise it will look dirty gray. Would be nice to switch fullScreen on and off for different views, still digging.