Implement preferences menu entry in MacCatalyst

I have an app which uses SwiftUI and Mac Catalyst. When running on a Mac I want to provide a preferences menu entry with the usual keyboard shortcut Command + ,. An implementation via the Settings bundle is out of question since my preferences are too complex for this.

Here is a reduced example of my implementation:

import SwiftUI

@main
struct PreferencesMenuTestApp: App {
  @UIApplicationDelegateAdaptor private var appDelegate: AppDelegate
  
  var body: some Scene {
    WindowGroup {
      ContentView()
    }
  }
}


class AppDelegate: UIResponder, UIApplicationDelegate {
  
  override func buildMenu(with builder: UIMenuBuilder) {
    let preferencesCommand = UIKeyCommand(title: "Preferences…",
                                          action: #selector(showPreferences),
                                          input: ",",
                                          modifierFlags: .command)
    
//    let preferencesCommand = UIAction(title: "Preferences…") { action in
//      debugPrint("show preferences")
//    }
    
    let menu = UIMenu(title: "Preferences…",
                      options: .displayInline,
                      children: [preferencesCommand])
    
    builder.insertSibling(menu, afterMenu: .about)
  }
  
  
  @objc
  func showPreferences() {
    debugPrint("show preferences")
  }
}

The problem is that the menu entry is disabled. Obviously the provided selector is not recognised. When I mark the AppDelegate with @main, then the menu entry is enabled. Of course then the app's window is empty. When I switch to the UIAction implementation (the out commented code) it works fine. But since one cannot provide a keyboard shortcut for UIActions this is not a good solution.

What am I missing? How would one implement a preferences menu entry that actually works?