I’m going to post the hole code so you can test yourself.
I don’t get why the victory condition for player 2 is not triggered in the if statement.
I know that is cause the if statement, maybe I wrote it wrong but is like 2 hourse that I’m on it and I don’t get what’s wrong with the statement.
Works fine for player 1.

private static void ticTacToe()
        {
            string[,] board = new string[3, 3];
            for (int i = 0; i < board.GetLength(0); i++)
                for (int j = 0; j < board.GetLength(1); j++)
                    board[i, j] = "-";
            string player1 = "X";
            string player2 = "O";
            string currentPlayer;
            int round = 1;
            int aX = 0;
            int aY = 0;
            bool flag = false;
            bool victory = false;
            while (flag == false || victory == false)
            {
                if (round == 1)
                {
                    currentPlayer = player1;
                    round++;
                }
                else
                {
                    currentPlayer = player2;
                    round--;
                }

                bool valid = false;
                while (valid == false)
                {
                    bool validCord = false;
                    while (validCord == false)
                    {
                        Console.Write("Where to put(X Co)?: ");
                        aX = int.Parse(Console.ReadLine());
                        Console.Write("Where to put(Y Co)?: ");
                        aY = int.Parse(Console.ReadLine());

                        if(0 <= aX && aX <= 2 && 0 <= aY && aY <= 2)
                        {
                            validCord = true;
                        }
                    }
                    

                    if (board[aY, aX] == "-")
                    {
                        valid = true;
                        board[aY, aX] = currentPlayer;
                    }

                }
                
                for (int i = 0; i < board.GetLength(0); i++)
                {
                    for (int j = 0; j < board.GetLength(1); j++)
                    {
                        Console.Write(board[i, j]);

                        if (board[i, j] != "-")
                        {
                            flag = true;
                        }
                        else
                        {
                            flag = false;
                        }
                    }
                    Console.WriteLine();
                }
                //|||
                if ((board[0, 0] == "X" && board[1, 0] == "X" && board[2, 0] == "X") || (board[0, 0] == "Y" && board[1, 0] == "Y" && board[2, 0] == "Y"))
                {
                    victory = true;
                    Console.Write(victory + " Victory for player " + currentPlayer);
                }
                else if ((board[0, 1] == "X" && board[1, 1] == "X" && board[2, 1] == "X") || (board[0, 1] == "Y" && board[1, 1] == "Y" && board[2, 1] == "Y"))
                {
                    victory = true;
                    Console.Write(victory + " Victory for player " + currentPlayer);
                }
                else if ((board[0, 2] == "X" && board[1, 2] == "X" && board[2, 2] == "X") || (board[0, 2] == "Y" && board[1, 2] == "Y" && board[2, 2] == "Y"))
                {
                    victory = true;
                    Console.Write(victory + " Victory for player " + currentPlayer);
                }
                //---
                else if ((board[0, 0] == "X" && board[0, 1] == "X" && board[0, 2] == "X") || (board[0, 0] == "Y" && board[0, 1] == "Y" && board[0, 2] == "Y"))
                {
                    victory = true;
                    Console.Write(victory + " Victory for player " + currentPlayer);
                }
                else if ((board[1, 0] == "X" && board[1, 1] == "X" && board[1, 2] == "X") || (board[1, 0] == "Y" && board[1, 1] == "Y" && board[1, 2] == "Y"))
                {
                    victory = true;
                    Console.Write(victory + " Victory for player " + currentPlayer);
                }
                else if ((board[2, 0] == "X" && board[2, 1] == "X" && board[2, 2] == "X") || (board[2, 0] == "Y" && board[2, 1] == "Y" && board[2, 2] == "Y"))
                {
                    victory = true;
                    Console.Write(victory + " Victory for player " + currentPlayer);
                }
                //X
                else if ((board[0, 0] == "X" && board[1, 1] == "X" && board[2, 2] == "X") || (board[0, 0] == "Y" && board[1, 1] == "Y" && board[2, 2] == "Y"))
                {
                    victory = true;
                    Console.Write(victory + " Victory for player " + currentPlayer);
                }
                else if ((board[0, 2] == "X" && board[1, 1] == "X" && board[2, 0] == "X") || (board[0, 2] == "Y" && board[1, 1] == "Y" && board[2, 0] == "Y"))
                {
                    victory = true;
                    Console.Write(victory + " Victory for player " + currentPlayer);
                }
            }
            Console.ReadLine();

        }

>Solution :

At the top of your code, you have these definitions for player1 and player2:

string player1 = "X";
string player2 = "O";

However, all of your if statements look like this:

if ((board[0, 0] == "X" && board[1, 0] == "X" && board[2, 0] == "X") || (board[0, 0] == "Y" && board[1, 0] == "Y" && board[2, 0] == "Y"))

You’re checking for X and Y instead of X and O, hence why the win condition is never triggered for player2.