Find can only be called from the main thread
And an error will appear on the console
If you'd like, I'd like you to give me a solution why I get an error.
Debug was done. The boss in the solution
If i reference the text object in Start and change the value in Update
I said I could do it, but I didn't understand it well.
Can you tell me if you like?

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using System.Net;
using System.Net.Sockets;
using System.Threading;
using UnityEngine.UI;//<---- Add 1

public class UdpSocket: MonoBehaviour
{
private string _MulticastAddr ="224.0.23.0" ;;// multicast address
private string _RemoteHost ="" ;;// Sender address
private int _SendPort = 3610;// send port
private int _RecvPort = 3610;// Receive port

private UdpClient _UdpClient;// UDP
private IPEndPoint _IpEndPoint;// IPEndPoint
private Thread _RecvThread;// receive thread

// Connect
public void Connect ()
{
IPAddress grpAddr = IPAddress.Parse (_MulticastAddr);

if (_IpEndPoint! = null) _IpEndPoint = null;
_IpEndPoint = new IPEndPoint (grpAddr, _RecvPort);

// Join a multicast group
Disconnect ();
_UdpClient = new UdpClient (_RecvPort);
_UdpClient.JoinMulticastGroup (grpAddr);

// Create receive thread
_RecvThread = new Thread (ReceiveMulticastThread);
_RecvThread.Start ();

// Send node profile notification
SendNodeProfile ();
}

// Disconnect
public void Disconnect ()
{
if (_RecvThread! = null)
{
_RecvThread.Abort ();
_RecvThread = null;
}

if (_UdpClient! = null)
{
IPAddress grpAddr = IPAddress.Parse (_MulticastAddr);
_UdpClient.DropMulticastGroup (grpAddr);
_UdpClient.Close ();
_UdpClient = null;
}
}

// Send node profile notification
public void SendNodeProfile ()
{
byte [] pack = BuildNodeProfileInfo ();
SendPacket (pack, _MulticastAddr);
}

// Send
public void SendPacket (byte [] packet, string host)
{
_UdpClient.Send (packet, packet.Length, host, _SendPort);
}

// Receiving thread
public void ReceiveMulticastThread ()
{
byte [] packet;

int i = 0;

System.Text.StringBuilder s = new System.Text.StringBuilder ();

while (true)
{
packet = _UdpClient.Receive (ref _IpEndPoint);
if (packet! = null)
{
// Received!
s.Remove (0, s.Length);
for (i = 0;i<packet.Length;i ++)
{
s.Append (System.Convert.ToString (packet [i], 16) .PadLeft (2,'0'));
}

Debug.Log (s.ToString ());

Text targetText;//<---- Add 2
GameObject _Object;
_Object = GameObject.Find ("Text");

targetText = _Object.GetComponent<Text>();//<---- Add 3
targetText.text ="s.ToString ()" ;;//<---- add 4

}
}
}

// Create node profile notification packet
private byte [] BuildNodeProfileInfo ()
{
byte [] pack;
pack = new byte [17];

pack [0] = 0x10;// EHD1
pack [1] = 0x81;// EHD2
pack [2] = 0x00;//
pack [3] = 0x01;// ID

pack [4] = 0x0E;// Source "Node Profile Class"
pack [5] = 0xF0;// EOJ = 0x0E F0 01
pack [6] = 0x01;//

pack [7] = 0x0E;// Destination "node profile class"
pack [8] = 0xF0;// EOJ = 0x0E F0 01
pack [9] = 0x01;//

pack [10] = 0x73;// ESV

pack [11] = 0x01;// OPC

pack [12] = 0xD5;// EPC
pack [13] = 0x04;// PDC
pack [14] = 0x01;// EDT
pack [15] = 0x05;//
pack [16] = 0xFF;//
pack [16] = 0x01;//

return pack;
}
}

Code
`` `