Can't make tic-tac-toe medium and hard difficulty levels?

Question

C++ / C#

I can't make two difficulty levels for tic-tac-toe. I made an easy one with the help of a random house that selects cells and checks if there is a sign there and sets it depending on the choice of the player's sign.
Here is the easy code:

using System.Collections;
using System.Collections.Generic;
using System.Threading;
using UnityEngine;
using UnityEngine.UI;
 
public class EasyBot : MonoBehaviour
{
    public Text[] tbs;
    public float timerX = 1f;
    public float timerO = 1f;
 
    void Update()
    {
        BotControls();
    }
    void BotControls()
    {
        if (ChoosingXorO.botxoro == "X" && WhoseMove.whosemove == "X")
        {
            timerX -= Time.deltaTime;
            int rand_tbX = Random.Range(0, 9);
            if(tbs[rand_tbX].text != "X" && tbs[rand_tbX].text != "O")
            {
                if(timerX <= 0)
                {
                    tbs[rand_tbX].text = "X";
                    WhoseMove.whosemove = "O";
                    timerX = 1f;
                }
            }
        }
        if(ChoosingXorO.botxoro == "O" && WhoseMove.whosemove == "O")
        {
            timerO -= Time.deltaTime;
            int rand_tbO = Random.Range(0, 9);
            if (tbs[rand_tbO].text != "X" && tbs[rand_tbO].text != "O")
            {
                if(timerO <= 0)
                {
                    tbs[rand_tbO].text = "O";
                    WhoseMove.whosemove = "X";
                    timerO = 1f;
                }
            }
        }
    }
}

if not difficult tell me how to make medium and hard difficulty levels

Answer 1

tic-tac-toe is a game with complete information, and is "solved" through

tree of game situations in accordance with the mini-max method. The total number of nodes in such a tree is 255168

( wiki ). We take the alpha-beta clipping algorithm , and the level of complexity in this case will be set through the mini-max criterion, or more simply - by the depth of the viewed tree, and / or the number of viewed vertices