To listen to the route change events of AvAudioSession use the following observer.

 let notificationCenter = NotificationCenter.default
        notificationCenter.removeObserver(self)
       notificationCenter.addObserver(self,
                                       selector: #selector(routeChangeEventHandle),
                                       name: AVAudioSession.routeChangeNotification,
                                       object: nil)

Now add the handler used in the #selector:

@objc func routeChangeEventHandle(notification: Notification) {
        guard let userInfo = notification.userInfo,
            let reasonValue = userInfo[AVAudioSessionRouteChangeReasonKey] as? UInt,
            let reason = AVAudioSession.RouteChangeReason(rawValue: reasonValue) else {
                print("Interrupption not reason.");
                return
        }
         // Switch over the route change reason.
        switch reason {


        case .newDeviceAvailable: // New device found.
            print("RouteChangeReason: New Device found.");
        
        case .oldDeviceUnavailable: // Old device removed.
            print("RouteChangeReason: Old device unavailable.");
        
        case .categoryChange:
            let session = AVAudioSession.sharedInstance();
            print("session info:")
            print(session.currentRoute.debugDescription);
            print(session.category);
            print(session.currentRoute);
            print(session.mode);
            print(session.categoryOptions);
            print("RouteChangeReason: Category of av audio session has changed");
        
        case .override:
            print("RouteChangeReason: Category was overriden");
        
        case .wakeFromSleep:
            print("RouteChangeReason: Wake from sleep");
        
        case .noSuitableRouteForCategory:
            print ("RouteChangeReason: No suitable route for category");

        case .routeConfigurationChange:
            print ("RouteChangeReason: route configuration has been changed");
        default:
            print("RouteChangeReason: Unknown");
        }
    }

Cheers and Peace out.