TopViewController.swift

extension UIApplication {
    var topViewController: UIViewController? {
        if #available(iOS 13.0, *) {
            if UIApplication.shared.supportsMultipleScenes, let keyWindow = UIApplication.shared.windows.first(where: { $0.isKeyWindow }) {
                 return keyWindow.visibleViewController
            } else {
                return UIApplication.shared.keyWindow?.visibleViewController
            }
        } else {
            return UIApplication.shared.keyWindow?.visibleViewController
        }
    }
}

extension UIWindow {
    
    var visibleViewController: UIViewController? {
        guard let root = rootViewController else { return nil }
        return UIWindow.visibleViewController(from: root)
    }
    
    private class func visibleViewController(from vc: UIViewController) -> UIViewController {
        switch vc {
        case let navigationController as UINavigationController:
            return UIWindow.visibleViewController(from: navigationController.visibleViewController!)
            case let tabBarController as UITabBarController:
            return UIWindow.visibleViewController(from: tabBarController.selectedViewController!)
        default:
            if let presentedViewController = vc.presentedViewController {
                return UIWindow.visibleViewController(from: presentedViewController.presentedViewController!)
            } else {
                return vc;
            }
        }
    }
}