using System;

using System.Threading;

using System.Threading.Tasks;

public class Program

{

    static async Task Main()

    {

        //ДОБАВЛЕН AWAIT!!!!!!!!!!!

        await SomeMethodAsync1();//ТУТ ДОБАВЛЕН AWAIT!!!!!!!!!!!

        Console.WriteLine($"ThrID={Thread.CurrentThread.ManagedThreadId}");

        for (int i = 0; i < 5; i++)

        {

            Console.WriteLine($"MAIN Iter={i}");

            Thread.Sleep(100);

        }

    }

​

    static async Task SomeMethodAsync1()

    {

        Console.WriteLine($"TrID={Thread.CurrentThread.ManagedThreadId}");  // <== Добавлено

        await Task.Yield();

        Console.WriteLine($"TrID={Thread.CurrentThread.ManagedThreadId}");

        for (int i = 0; i < 5; i++)

        {

            Console.WriteLine($"MethodIter={i}");

            Thread.Sleep(100);

        }

    }

}