SwiftUI_Mac_BackButton.swift

import SwiftUI

struct BackButton: View {
    @State private var table: NSMapTable<NSString, NSWindow> = .strongToWeakObjects()
    
    var body: some View {
        Button("Back") { 
            let visibleItems: [NSToolbarItem] = (table.object(forKey: "window")?.toolbar?.visibleItems)!
            let backItem = visibleItems.first(where: { $0.itemIdentifier.rawValue == "com.apple.SwiftUI.navigationStack.back" })!
            
            // SwiftUI.SwiftUISegmentedControl
            let control = backItem.view!.subviews.first!.subviews.first! as! NSSegmentedControl
            
            let target = control.target!
            let action = control.action!
            
            _ = target.perform(action, with: nil)
        }
        .onWindowChange { window in
            table.setObject(window, forKey: "window")
        }
    }
}

struct WindowReader: NSViewRepresentable {
    let windowHandler: @MainActor (NSWindow?) -> Void
    
    func makeNSView(context: Context) -> ContentView {
        ContentView(windowHandler: windowHandler)
    }
    
    func updateNSView(_ nsView: ContentView, context: Context) {
        nsView.windowHandler = windowHandler
    }
    
    final class ContentView: NSView {
        var windowHandler: @MainActor (NSWindow?) -> Void
        
        init(windowHandler: @escaping (NSWindow?) -> Void) {
            self.windowHandler = windowHandler
            super.init(frame: .zero)
        }
        
        required init?(coder: NSCoder) {
            fatalError("init(coder:) has not been implemented")
        }
        
        override func viewDidMoveToWindow() {
            super.viewDidMoveToWindow()
            windowHandler(window)
        }
    }
}

extension View {
    func onWindowChange(_ windowHandler: @escaping (NSWindow?) -> Void) -> some View {
        self
            .overlay { 
                WindowReader(windowHandler: windowHandler)
            }
    }
}