throttle.cs

using Polly;

var pipeline = new ResiliencePipelineBuilder<HttpResponseMessage>()
    .AddConcurrencyLimiter(permitLimit: 10, queueLimit: 100)
    .Build();

var httpClient = new HttpClient();

await Parallel.ForEachAsync(Enumerable.Range(0, 10).ToArray(), async (i, _) =>   
{
    var response = await pipeline.ExecuteAsync<HttpResponseMessage>(async _ => await httpClient.GetAsync("https://google.ca"));
    Console.WriteLine($"Iteration: {i}, Response: {response.StatusCode}");
});

Console.WriteLine("Done");