Blur app when resigning active

AppDelegate.swift

class AppDelegate: UIResponder, UIApplicationDelegate {
    var window: UIWindow?

    func applicationWillResignActive(_ application: UIApplication) {
        addBlurViews()
    }

    func applicationDidBecomeActive(_ application: UIApplication) {
        removeBlurViews()
    }
}

private extension AppDelegate {
    var blurViewTag: Int {
        return 999999
    }

    func addBlurViews() {
        for window in UIApplication.shared.windows {
            let blurEffect: UIBlurEffect
            if #available(iOS 13.0, *) {
                blurEffect = UIBlurEffect(style: .systemUltraThinMaterial)
            } else {
                blurEffect = UIBlurEffect(style: .light)
            }
            let blurEffectView = UIVisualEffectView(effect: blurEffect)
            blurEffectView.frame = window.frame
            blurEffectView.autoresizingMask = [.flexibleWidth, .flexibleHeight]
            blurEffectView.tag = blurViewTag
            window.addSubview(blurEffectView)
        }
    }

    func removeBlurViews() {
        for window in UIApplication.shared.windows {
            if let blurView = window.viewWithTag(blurViewTag) {
                blurView.removeFromSuperview()
            }
        }
    }
}

thank