Reproduction for Microsoft.Data.SqlClient deadlocking issue https://github.com/dotnet/SqlClient/issues/1124

PrepareFailTest.csproj

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFrameworks>net472</TargetFrameworks>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="Microsoft.Data.SqlClient" Version="2.1.3" />
    <Reference Include="System.Transactions" />
  </ItemGroup>

</Project>

Program.cs

using Microsoft.Data.SqlClient;
using System;
using System.Threading.Tasks;
using System.Transactions;

namespace PrepareFailTest
{
    class Program
    {
        static string connStr = @"Data Source=.\SQLEXPRESS;Initial Catalog=master;Integrated Security=True;";
        static readonly TransactionOptions transactionOptions = new TransactionOptions
        {
            IsolationLevel = IsolationLevel.ReadCommitted,
            Timeout = TransactionManager.DefaultTimeout
        };

        public static async Task Main()
        {
            try
            {
                using (var scope = new TransactionScope(TransactionScopeOption.RequiresNew, transactionOptions, TransactionScopeAsyncFlowOption.Enabled))
                {
                    using (var conn = new SqlConnection(connStr))
                    {
                        await conn.OpenAsync();
                        Transaction.Current.EnlistDurable(EnlistmentWhichFailsDuringPrepare.Id, new EnlistmentWhichFailsDuringPrepare(), EnlistmentOptions.None);
                        scope.Complete();
                    }
                }
            }
            catch (Exception x)
            {
                Console.WriteLine(x.Message);
            }

            Console.WriteLine("Test run complete");
        }
    }

    class EnlistmentWhichFailsDuringPrepare : IEnlistmentNotification
    {
        public static readonly Guid Id = Guid.NewGuid();
        // fail during prepare, this will cause scope.Complete to throw
        public void Prepare(PreparingEnlistment preparingEnlistment) => preparingEnlistment.ForceRollback();
        public void Commit(Enlistment enlistment) => enlistment.Done();
        public void Rollback(Enlistment enlistment) => enlistment.Done();
        public void InDoubt(Enlistment enlistment) => enlistment.Done();
    }
}