NBitcoin Transaction sign(secret, bool) is giving error. Instead of bool it says to pass Coin Object
Sign method expects two arguments: private key and coins to be spent
false makes no sense in that line according to the documentation mentioned in the below link but I found similar code in another question NBitcoin: signing a transaction in TestNet so I will have to try on my system in VS 2019:
https://programmingblockchain.gitbook.io/programmingblockchain/bitcoin_transfer/spend_your_coin#sign-your-transaction

transaction.Sign(bitcoinPrivateKey, receivedCoins.ToArray());

UPDATE(I tried the below things and it worked for me):
Create a Private key and get address:

Send some amount to the address: https://blockstream.info/testnet/tx/6266c8262610ab0790f9f1841930bb27666588be8ab343a7e0470b7bb48a655b
Use the below code to create a Tx, sign and broadcast it:

            var bitcoinPrivateKey = new BitcoinSecret("cPof7e5g6xfgB6AZrc6XVTVwA4efLJurh9kVxa6FRChbr8Jyqaon", Network.TestNet);
            var network = bitcoinPrivateKey.Network;
            var address = bitcoinPrivateKey.GetAddress(ScriptPubKeyType.Legacy);

            var client = new QBitNinjaClient(network);
            var transactionId = uint256.Parse("6266c8262610ab0790f9f1841930bb27666588be8ab343a7e0470b7bb48a655b");
            var transactionResponse = client.GetTransaction(transactionId).Result;


            var receivedCoins = transactionResponse.ReceivedCoins;
            OutPoint outPointToSpend = null;
            foreach (var coin in receivedCoins)
            {
                if (coin.TxOut.ScriptPubKey == bitcoinPrivateKey.ScriptPubKey)
                {
                    outPointToSpend = coin.Outpoint;
                }
            }

            var transaction = Transaction.Create(network);
            transaction.Inputs.Add(new TxIn()
            {
                PrevOut = outPointToSpend
            });

            var myAddress = BitcoinAddress.Create("tb1q5va20jy9dg30zdyy0nakg5y95trdr3gtw5jy9d", Network.TestNet);

            
            var txOutAmount = new Money(0.01m, MoneyUnit.BTC);

            // Tx fee
            var minerFee = new Money(0.0005m, MoneyUnit.BTC);

            // Change
            var txInAmount = (Money)receivedCoins[(int)outPointToSpend.N].Amount;
            var changeAmount = txInAmount - txOutAmount - minerFee;

            transaction.Outputs.Add(txOutAmount, myAddress.ScriptPubKey);
            transaction.Outputs.Add(changeAmount, bitcoinPrivateKey.ScriptPubKey);

           
            transaction.Inputs[0].ScriptSig = address.ScriptPubKey;

            //Sign Tx
            transaction.Sign(bitcoinPrivateKey, receivedCoins.ToArray());

            //Broadcast Tx
            BroadcastResponse broadcastResponse = client.Broadcast(transaction).Result;

            if (!broadcastResponse.Success)
            {
                Console.Error.WriteLine("ErrorCode: " + broadcastResponse.Error.ErrorCode);
                Console.Error.WriteLine("Error message: " + broadcastResponse.Error.Reason);
            }
            else
            {
                Console.WriteLine("Success! Tx:");
                Console.WriteLine(transaction.GetHash());
            }


Tx: https://blockstream.info/testnet/tx/0ada6696fb134ebc4f96a55a3d5b60d90e5a723ec2e27634bb1777730e7df914