How do I get an asynchronous method to work correctly in a parallel loop in C#? [duplicate]

Question

I have the code below that uses HttpClient to download content for a series of websites. However, whilst a synchronous inner function works fine in the Parallel.ForEach, I have been unable to get the asychronous version to work.

I would appreciate to know how to resolve this and how the code should look.

The code is a simple console app. However, I have been unable to get this to work at all (synchronous or async) in a Windows Form app. Can anyone explain why this is so?

Code:

using DLWeb;
using System.Collections.Concurrent;
 
// initialize test data
ConcurrentBag<Website> _websites = [ new Website("BBC", "https://www.bbc.co.uk"),
                                     new Website("Google", "https://www.google.com"),
                                     new Website("Amazon","https://www.amazon.com")];
// set mode
bool USE_DOWNLOAD_ASYNC = true;

string mode = USE_DOWNLOAD_ASYNC ? "Asynchronously" : "Synchronously";
Console.WriteLine($"Starting (Running Download {mode})...{Environment.NewLine}");

ParallelLoopResult _loopRes = new();

if (USE_DOWNLOAD_ASYNC) // Async 
{
    await Task.Run(() =>
    {
        _loopRes = Parallel.ForEach<Website>(_websites, async (item) =>
        {
            var res = await DownloadAsync(item);
            item.Content = res;
        });
    });
}
else
{
    await Task.Run(() =>
    {
        _loopRes = Parallel.ForEach<Website>(_websites, (item) =>
        {
            string s = "";

            s = Download(item.URL);
            item.Content = s;
        });
    });
}

if (_loopRes.IsCompleted)
{
    foreach (var item in _websites)
    {
        Console.WriteLine($"{item.Name}: {item.Content.Length}{Environment.NewLine}");
    }

    Console.WriteLine("Done.");
}

Console.ReadKey();

// ----------------------------------------------------

static string Download(string site)
{
    HttpClient httpClient = new();

    var r = httpClient.GetStringAsync(site).Result;

    return r;
}

async static Task<string> DownloadAsync(Website item)
{
    HttpClient httpClient = new();
    string res;
    res = "" + await httpClient.GetStringAsync(item.URL);
    return res;
}

The Website class:

 public class Website
 {
     public string Name { get; set; } = "";
     public string URL { get; set; } = "";
     public string Content { get; set; } = "";

     public Website()
     {
     }

     public Website(string name, string url)
     {
         Name = name;
         URL = url;
     }
 } 

Any help appreciated.