This is expected, as the ITypedHttpClientFactory documentation states:

The default ITypedHttpClientFactory<TClient> uses type activation to create typed client instances. Typed client types are not retrieved directly from the IServiceProvider. See CreateInstance(IServiceProvider, Type, Object[]) for details.

So, here’s answer to your question:

Typed client types are not retrieved directly from the IServiceProvider.

One way to solve this problem is to inject a named client into the typed client via the ITypedHttpClientFactory‘s CreateClient method. Whenever you fetch a named HttpClient then it will retrieve it from the DI with all of its DelegatingHandlers.

Here you can find a working example: https://dotnetfiddle.net/wC4Neg

Service registrations

ServiceCollection collection  = new();
collection.AddTransient<TestDelegatingHandler>();
collection.AddHttpClient();
collection.AddHttpClient<ITypedClient, TypedClient>("test")
    .AddHttpMessageHandler(sp => sp.GetService<TestDelegatingHandler>());

• Here we register a dummy DelegatingHandler into the DI container first
• Then we register the default HttpClient factories
• Finally we register a typed client which is named test
  • Here we add the MessageHandler to the named client

Client creations

ServiceProvider provider = collection.BuildServiceProvider();
IHttpClientFactory namedFactory = provider.GetRequiredService<IHttpClientFactory>();
ITypedHttpClientFactory<TypedClient> typedFactory  = provider.GetRequiredService<ITypedHttpClientFactory<TypedClient>>();

HttpClient namedClient = namedFactory.CreateClient("test");
TypedClient typedClient = typedFactory.CreateClient(namedClient); 

• First we build the ServiceCollection
• Then we retrieve an IHttpClientFactory and an ITypedHttpClientFactory service
• Thirdly we fetch the named client .CreateClient("test")
  • This client is decorated with the dummy DelegatingHandler
• Finally we create a TypedClient instance via the ITypedHttpClientFactory by injecting the previously fetched named HttpClient

Supporting structures

public interface ITypedClient
{
    Task GetAsync();
}

public class TypedClient: ITypedClient
{
    private readonly HttpClient _client;
    public TypedClient(HttpClient client) => _client = client;
    
    public async Task GetAsync() => await _client.GetAsync("http://stackoverflow.com");
}

public class TestDelegatingHandler: DelegatingHandler
{
    protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
    {
        "Hello".Dump();
        return await base.SendAsync(request, cancellationToken);
    }
}