iOS 13: Swift - 'Set application root view controller programmatically' does not work

Question

I have following code in my AppDelegate.swift to setup root view controller for an iOS application. But it does not work. It follows Target structure (defined under General

Answer 1

    let MainViewController  = mainStoryboard.instantiateViewController(withIdentifier: "MainViewController") as! MainViewController

                    let nvc:rootNavigation  = mainStoryboard.instantiateViewController(withIdentifier: "rootNavigation") as! rootNavigation
                    nvc.viewControllers = [Mainmap]
                   
                    leftViewController.mainViewController = nvc

UIApplication.shared.windows.first?.backgroundColor = UIColor(red: 236.0, green: 238.0, blue: 241.0, alpha: 1.0)
                    UIApplication.shared.windows.first?.rootViewController = nvc
                    UIApplication.shared.windows.first?.makeKeyAndVisible()