Open/Close NSWindow from SwiftUI.View

View+NSWindow.swift

import SwiftUI

/**
 hack to avoid crashes on window close, and remove the window from the
 NSApplication stack, ie: avoid leaking window objects
 */
fileprivate final class WindowDelegate: NSObject, NSWindowDelegate {
    func windowShouldClose(_ sender: NSWindow) -> Bool {
        NSApp.removeWindowsItem(sender)
        return true
    }
    
    deinit {
        NSLog("deallocated ...")
    }
}

public extension View {
    func openInNewWindow(_ introspect: @escaping (_ window: NSWindow) -> Void) {
        let windowDelegate = WindowDelegate()
        let rv = NSWindow(
            contentRect: NSRect(x: 0, y: 0, width: 320, height: 320),
            styleMask: [.titled, .closable, .miniaturizable, .resizable, .fullSizeContentView],
            backing: .buffered,
            defer: false
        )
        rv.isReleasedWhenClosed = false
        rv.title = "New Window"
        // who owns who :-)
        rv.delegate = windowDelegate
        rv.contentView = NSHostingView(rootView: self)
        introspect(rv)
        rv.center()
        rv.makeKeyAndOrderFront(nil)
    }
}

WindowVanillaSwiftUIApp.swift

import SwiftUI

@main
struct WindowVanillaSwiftUIApp: App {
    var body: some Scene {
        WindowGroup {
            ContentView()
        }
    }
}

struct ContentView: View {
    var body: some View {
        Button(action: {
            ChildView().openInNewWindow { window in
                window.title = "Window title"
            }
        }) {
            Image(systemName: "paperplane")
        }
        .padding()
    }
}

struct ChildView: View {
    var body: some View {
        VStack {
            Spacer()
            HStack {
                Spacer()
                Text("Hello World")
                    .padding()
                Spacer()
            }
            Spacer()
            HStack {
                Spacer()
                Button(action: {
                    NSApp.keyWindow?.close()
                }) {
                    Text("Close")
                }
            }
            .padding()
        }
        .frame(minWidth: 640, minHeight: 480)
    }
}

struct ChildView_Previews: PreviewProvider {
    static var previews: some View {
        ChildView()
    }
}

If you are using TCA from pointfree.co
You can pass in a scoped store to that ChildView

        Button(action: {
            ChildView(store: self.store.scope(...)).openInNewWindow { window in
                window.title = "Window title"
            }
        }) {
            Image(systemName: "paperplane")
        }