On my app I use the typical way for biometric authentication after coming back from background:

@main
struct MyApp: App {
  @Environment(\.scenePhase) var phase

  var body: some Scene {
    WindowGroup {
      MainView()

      .onChange(of: phase) { (newPhase) in
          switch newPhase {
          case .active: 
              biometricsAuthentication()
          case .inactive: print("App is inactive")
          case .background: print("App is on background")
              appBlocked = true
          default: print("default")
          }
        }
      }
    }

Doing this way everything works OK, but there is a little moment MainView is visible BEFORE authentication method triggers, I supossed due to the fraction of time that app is .inactive, after coming back from .background.

On MacOS app version, I call this authentication method on AppDelegate "applicationDidFinishLaunching" method, and nothing at all is presented until authentication finishes. So, I've tried to emulate this on iOS, with a dedicated AppDelegate, and trying some methods, without success.

Is this the correct way of doing it? Is there a way to accomplish it?