Keeping SwiftUI window on top of all other apps (even in fullscreen)

Question

I maintain a custom clock app (just for me, not the app store) that I use to view the time on my computer. I want it to stay over all other windows, including apps (and videos) in fullscreen. When I updated to MacOS Sequoia (15.0) my old solution stopped working. I can still get the app to move to new spaces as I switch between them, but I cannot get a window to remain on the screen while transitioning another app to full screen. This is the minimum code I used to recreate the problem in a fresh SwiftUI app:

@main
struct testtickerApp: App {
    @NSApplicationDelegateAdaptor(AppDelegate.self) var appDelegate
    
    var body: some Scene {
        WindowGroup {
            ContentView()
        }
    }
}

class AppDelegate: NSObject, NSApplicationDelegate, NSWindowDelegate {
    func applicationDidFinishLaunching(_ notification: Notification) {
        let window = NSApplication.shared.windows.first!
        window.level = .floating
        window.styleMask = .borderless
        window.collectionBehavior = [.canJoinAllApplications, .canJoinAllSpaces, .auxiliary, .fullScreenAuxiliary, .ignoresCycle]
    }
}

and this is the code that used to work for me, prior to MacOS 15.0 (used in the same applicationDidFinishLaunching function):

func setupWindow(_ window: NSWindow) {
    window.titleVisibility = .hidden
    window.titlebarAppearsTransparent = true
    window.standardWindowButton(NSWindow.ButtonType.closeButton)?.isHidden = true
    window.standardWindowButton(NSWindow.ButtonType.miniaturizeButton)?.isHidden = true
    window.standardWindowButton(NSWindow.ButtonType.zoomButton)?.isHidden = true
    window.isOpaque = false
    window.hasShadow = false
    window.level = .floating
    window.backgroundColor = NSColor.clear
    window.isReleasedWhenClosed = false
    window.isMovableByWindowBackground = true
    window.collectionBehavior = .canJoinAllSpaces
    window.titlebarSeparatorStyle = .none
    window.ignoresMouseEvents = true
    window.delegate = self
}

based on these answers:

Enable fullscreen for floating window in macOS app

Why does my NSWindow not float above full screen apps when created programmatically? (Swift 5)

How to create whole screen overlay in MacOS with Swift?

Window visible on all spaces (including other fullscreen apps)

How to keep my overlay on top while another app is in Full Screen mode?

and the description of fullScreenAuxiliary, I would expect my previous solution to still work. Is this a bug? Is there any way to get this working? I have tried closing and redrawing the window, moving it to front, changing LSUIElement to TRUE in my info.plist, and many other things, with essentially no success. I don’t need the solution to be especially pretty (or within Apple’s guidelines), but I would like it to work.

Answer 1

With macOS 15 you can use .windowLevel(.floating) on your window to keep it floating on top of your desktop over all other windows:

@main
struct ExampleApp: App {
    var body: some Scene {
        WindowGroup {
            ContentView()
        }
        .windowLevel(.floating) // Use it here.
    }
}