Variable Menubar Icon app https://multi.app/blog/pushing-the-limits-nsstatusitem

VariableMenubar.swift

//Original article: https://multi.app/blog/pushing-the-limits-nsstatusitem

import SwiftUI
import Combine

@main
struct MenuBarApp: App {
    // Tie our custom AppDelegate into SwiftUI's lifecycle
    @NSApplicationDelegateAdaptor private var appDelegate: AppDelegate
    
    var body: some Scene {
        // We won't actually show a main window here, but SwiftUI requires a scene.
        // Using Settings for demonstration; you could also use .window if needed.
        Settings {
            EmptyView()
        }
    }
}

class AppDelegate: NSObject, NSApplicationDelegate {
    private let statusItemManager = StatusItemManager()
    
    func applicationDidFinishLaunching(_ notification: Notification) {
        // Create the status item once the app has finished launching
        statusItemManager.createStatusItem()
    }
}

// MARK: - StatusItemManager
final class StatusItemManager: ObservableObject {
    private var hostingView: NSHostingView<StatusItem>?
    private var statusItem: NSStatusItem?
    
    private var sizePassthrough = PassthroughSubject<CGSize, Never>()
    private var sizeCancellable: AnyCancellable?
    
    func createStatusItem() {
        // Use a variable-length status item
        let statusItem: NSStatusItem = NSStatusBar.system.statusItem(withLength: NSStatusItem.variableLength)
        
        // Create our SwiftUI view and wrap it in an NSHostingView
        let hostingView = NSHostingView(rootView: StatusItem(sizePassthrough: sizePassthrough))
        hostingView.frame = NSRect(x: 0, y: 0, width: 80, height: 24)
        
        // Place the hosting view inside the status item's button
        if let button = statusItem.button {
            button.frame = hostingView.frame
            button.addSubview(hostingView)
        }
        
        self.statusItem = statusItem
        self.hostingView = hostingView
        
        // Listen for size changes from the SwiftUI view
        sizeCancellable = sizePassthrough.sink { [weak self] size in
            let frame = NSRect(origin: .zero, size: .init(width: size.width, height: 24))
            self?.hostingView?.frame = frame
            self?.statusItem?.button?.frame = frame
        }
    }
}

// MARK: - A PreferenceKey to capture SwiftUI’s size
private struct SizePreferenceKey: PreferenceKey {
    static var defaultValue: CGSize = .zero
    static func reduce(value: inout CGSize, nextValue: () -> CGSize) {
        value = nextValue()
    }
}

// MARK: - The SwiftUI content shown in the status bar
struct StatusItem: View {
    var sizePassthrough: PassthroughSubject<CGSize, Never>
    @State private var showWave: Bool = false
    @State private var menuShown: Bool = false
    
    var body: some View {
        HStack(spacing: 0) {
            // First target
            Button {
                showWave.toggle()
            } label: {
                Text("Hello, world!")
                    .foregroundColor(.white)
            }
            .buttonStyle(StatusItemButtonStyle())
            
            // Second target, conditionally shown
            if showWave {
                Button {
                    menuShown.toggle()
                } label: {
                    Text("👋")
                }
                .buttonStyle(StatusItemButtonStyle())
                .popover(isPresented: $menuShown) {
                    Image(systemName: "hand.wave")
                        .resizable()
                        .frame(width: 100, height: 100)
                        .padding()
                }
            }
        }
        // Help SwiftUI compute the correct width
        .fixedSize()
        // Capture size changes via GeometryReader
        .overlay(
            GeometryReader { proxy in
                Color.clear.preference(key: SizePreferenceKey.self, value: proxy.size)
            }
        )
        // Send size changes through the PassthroughSubject
        .onPreferenceChange(SizePreferenceKey.self) { newSize in
            sizePassthrough.send(newSize)
        }
        // Provide a background color so white text is visible on a dark menu bar
        .padding(.horizontal, 8)
        .background(Color.blue)
    }
}

// MARK: - Custom Button Style
struct StatusItemButtonStyle: ButtonStyle {
    func makeBody(configuration: Self.Configuration) -> some View {
        configuration.label
            .padding(2)
            .frame(maxHeight: .infinity)
            .background(
                RoundedRectangle(cornerRadius: 4)
                    .fill(Color.white.opacity(configuration.isPressed ? 0.3 : 0.0))
            )
    }
}