AsyncMenu

Main main = new Main();

class Main
{
    private bool _isWorking = true;

    public Main()
    {
        Start();
    }

    private void Menu()
    {
        while (_isWorking == false)
        {
            Console.WriteLine("1.Начать");
            string userInput = Console.ReadLine();

            if (userInput == "1")
            {
                _isWorking = true;
                Start();
            }
        }
    }

    private async Task Start()
    {
        Task.Run(() => Write());

        while (_isWorking)
        {
            string userInput = Console.ReadLine();

            if (userInput == "1")
            {
                _isWorking = false;
            }
        }
        Menu();
    }

    private async Task Write()
    {
        while (_isWorking)
        {
            Console.WriteLine("1.Действие");
        }
    }
}