public class Program
{
   private const string SerialPortId = "COM6";

   public static void Main()
   {
      SerialDevice serialDevice;

      Debug.WriteLine("devMobile.IoT.SeeedLoRaE5.ShieldSerial starting");

      Debug.WriteLine(Windows.Devices.SerialCommunication.SerialDevice.GetDeviceSelector());

      try
      {
         serialDevice = SerialDevice.FromId(SerialPortId);

         // set parameters
         serialDevice.BaudRate = 9600;
         serialDevice.Parity = SerialParity.None;
         serialDevice.StopBits = SerialStopBitCount.One;
         serialDevice.Handshake = SerialHandshake.None;
         serialDevice.DataBits = 8;

         serialDevice.ReadTimeout = new TimeSpan(0, 0, 30);
         serialDevice.WriteTimeout = new TimeSpan(0, 0, 4);

         DataWriter outputDataWriter = new DataWriter(serialDevice.OutputStream);

#if SERIAL_SYNC_READ
         DataReader inputDataReader = new DataReader(serialDevice.InputStream);
#else
         serialDevice.DataReceived += SerialDevice_DataReceived;
#endif

         // set a watch char to be notified when it's available in the input stream
         // This doesn't appear to work with synchronous calls
         serialDevice.WatchChar = '\n';

         while (true)
         {
            uint bytesWritten = outputDataWriter.WriteString("AT+VER\r\n");
            Debug.WriteLine($"TX: {outputDataWriter.UnstoredBufferLength} bytes to output stream.");

            // calling the 'Store' method on the data writer actually sends the data
            uint txByteCount = outputDataWriter.Store();
            Debug.WriteLine($"TX: {txByteCount} bytes via {serialDevice.PortName}");

#if SERIAL_SYNC_READ
            uint bytesRead = inputDataReader.Load(50);

            Debug.WriteLine($"RXs :{bytesRead} bytes read from {serialDevice.PortName}");

            if (bytesRead > 0)
            {
               String response = inputDataReader.ReadString(bytesRead);
               Debug.WriteLine($"RX sync:{response}");
            }
#endif

            Thread.Sleep(20000);
         }
      }
      catch (Exception ex)
      {
         Debug.WriteLine(ex.Message);
      }
   }

   private static void SerialDevice_DataReceived(object sender, SerialDataReceivedEventArgs e)
   {
      switch (e.EventType)
      {
         case SerialData.Chars:
            //Debug.WriteLine("RX SerialData.Chars");
            break;

         case SerialData.WatchChar:
             Debug.WriteLine("RX: SerialData.WatchChar");
             SerialDevice serialDevice = (SerialDevice)sender;

            using (DataReader inputDataReader = new DataReader(serialDevice.InputStream))
            {
               inputDataReader.InputStreamOptions = InputStreamOptions.Partial;

               // read all available bytes from the Serial Device input stream
               uint bytesRead = inputDataReader.Load(serialDevice.BytesToRead);

               Debug.WriteLine($"RXa: {bytesRead} bytes read from {serialDevice.PortName}");

               if (bytesRead > 0)
               {
                  String response = inputDataReader.ReadString(bytesRead);
                  Debug.WriteLine($"RX:{response}");
               }
            }
            break;
         default:
            Debug.Assert(false, $"e.EventType {e.EventType} unknown");
            break;
      }
   }
}

The thread '<No Name>' (0x2) has exited with code 0 (0x0).
devMobile.IoT.SeeedLoRaE5.ShieldSerial starting
Ports available: COM5,COM6
TX: 8 bytes to output stream.
TX: 8 bytes via COM6
TX: 8 bytes to output stream.
TX: 8 bytes via COM6
RX: SerialData.WatchChar
RXa: 28 bytes read from COM6
RX:+VER: 4.0.11
+VER: 4.0.11

TX: 8 bytes to output stream.
TX: 8 bytes via COM6
RX: SerialData.WatchChar
RXa: 14 bytes read from COM6
RX:+VER: 4.0.11

TX: 8 bytes to output stream.
TX: 8 bytes via COM6
RX: SerialData.WatchChar
RXa: 14 bytes read from COM6
RX:+VER: 4.0.11

TX: 8 bytes to output stream.
TX: 8 bytes via COM6
RX: SerialData.WatchChar
RXa: 14 bytes read from COM6
RX:+VER: 4.0.11