Module Program

    Async Function Main(args As String()) As Task
        Dim count = 100
        Dim url = "foo.bar.baz"
        Dim tasks As New List(Of Task(Of String))

        For i = 0 To count - 1
            tasks.Add(DoRequest(url))
        Next

        Dim whenAll = Task.WhenAll(tasks)
        Dim results = Await whenAll

        ' В results у нас массив результатов всех запросов
        For Each r In results
            Console.WriteLine(r)
        Next
    End Function

    Async Function DoRequest(url As String) As Task(Of String)
        Dim webRequest = HttpWebRequest.Create(url)
        Using response = Await webRequest.GetResponseAsync()
            Using stream = response.GetResponseStream()
                Using reader = New StreamReader(stream)
                    ' Здесь можно сделать что-то с результатом отдельного запроса
                    Return Await reader.ReadToEndAsync()
                End Using
            End Using
        End Using
    End Function

End Module

Module Program

    Sub Main(args As String())
        Dim count = 100
        Dim url = "foo.bar.baz"
        Dim tasks As New List(Of Task)

        For i = 0 To count - 1
            tasks.Add(DoRequest(url))
        Next

        Dim whenAll = Task.WhenAll(tasks)
        whenAll.Wait()
    End Function

    Async Function DoRequest(url As String) As Task
        Dim webRequest = HttpWebRequest.Create(url)
        Using response = Await webRequest.GetResponseAsync()
            Using stream = response.GetResponseStream()
                Using reader = New StreamReader(stream)
                    Dim result = Await reader.ReadToEndAsync()
                    ' Запускаем обработку результата запроса
                    Await Task.Run(Sub
                        HandleRequestResult(result)
                    End Sub)
                End Using
            End Using
        End Using
    End Function

    Sub HandleRequestResult(result As String)
        ' Здесь какая-нибудь долгая обработка запроса
    End Function
End Module

ServicePointManager.ServerCertificateValidationCallback = (_, _, _, _) => true;

Stopwatch sw = new();

// тут параллелим на 100 потоков
sw.Reset();
sw.Start();
await Task.WhenAll(Enumerable.Repeat(0, 100).Select(__ =>
    Task.Run(() => {
        // в каждом потоке 1 синхронный запрос
        var request = HttpWebRequest.Create("https://sql.ru");
        using var response = request.GetResponse();
        using var stream = response.GetResponseStream();
        using StreamReader reader = new StreamReader(stream);
        _ = reader.ReadToEnd();
    })));
sw.Stop();
Console.WriteLine($"Сто потоков: {sw.ElapsedMilliseconds}");

// тут все просто асинхронно
sw.Reset();
sw.Start();
await Task.WhenAll(Enumerable.Repeat(0, 100).Select(async __ => {
    var request = HttpWebRequest.Create("https://sql.ru");
    using var response = await request.GetResponseAsync();
    using var stream = response.GetResponseStream();
    using StreamReader reader = new StreamReader(stream);
    _ = await reader.ReadToEndAsync();
}));
sw.Stop();
Console.WriteLine($"Сто запросов асинхронно: {sw.ElapsedMilliseconds}");

private async void button1_Click(object sender, EventArgs e)
{
    ServicePointManager.ServerCertificateValidationCallback = (_1, _2, _3, _4) => true;
    ServicePointManager.DefaultConnectionLimit = 5;

    Stopwatch sw = new Stopwatch();

    // тут параллелим на 100 потоков
    sw.Reset();
    sw.Start();
    await Task.WhenAll(Enumerable.Repeat(0, 100).Select(__ =>
        Task.Run(() => {
            // в каждом потоке 1 синхронный запрос
            var request = HttpWebRequest.Create("https://sql.ru");
            using var response = request.GetResponse();
            using var stream = response.GetResponseStream();
            using StreamReader reader = new StreamReader(stream);
            _ = reader.ReadToEnd();
        }))).ConfigureAwait(true);
    sw.Stop();
    // Console.WriteLine($"Сто потоков: {sw.ElapsedMilliseconds}");
    label1.Text = $"Сто потоков: {sw.ElapsedMilliseconds}";

    // тут все просто асинхронно
    sw.Reset();
    sw.Start();
    await Task.WhenAll(Enumerable.Repeat(0, 100).Select(async __ => {
        var request = HttpWebRequest.Create("https://sql.ru");
        using var response = await request.GetResponseAsync().ConfigureAwait(false);
        using var stream = response.GetResponseStream();
        using StreamReader reader = new StreamReader(stream);
        _ = await reader.ReadToEndAsync().ConfigureAwait(false);
    })).ConfigureAwait(true);
    sw.Stop();
    // Console.WriteLine($"Сто запросов асинхронно: {sw.ElapsedMilliseconds}");
    label2.Text = $"Сто запросов асинхронно: {sw.ElapsedMilliseconds}";
}