Or with build-time source generation (because this specific pattern of reflection is AOT-unfriendly). It's not as convenient if you are using default serializer options, but if you don't - it ties together JsonTypeInfo<T> and JsonSerializerOptions, so it ends up being a slightly terser way to write it. I do prefer the Rust-style serde annotations however.

  record User(string Name, DateOnly DoB);

  [JsonSerializable(typeof(User))]
  partial class SerializerContext: JsonSerializerContext;

  ...
  var user = new User("John", new(1984, 1, 1));
  var response = await http.PostAsJsonAsync(
    url, user, SerializerContext.Default.User);