Answer

After talking with other folks at the community I have opted for separating the User into a struct, in its own module, inside an OrderInfo directory:

lib/
  order_info/
    user.ex
  order_info.ex

I personally find this works great for readability. So for readability purposes this is what I ended up with:

defmodule AuctionHouse.Data.OrderInfo.User do
  @moduledoc """
  Represents the account information for a User.
  """

  use TypedStruct

  alias AuctionHouse.Shared.Utils

  @type user :: %{
          (ingame_name :: String.t()) => String.t(),
          (status :: String.t()) => String.t()
        }

  typedstruct enforce: true do
    @typedoc "Account information of an User"

    field(:ingame_name, String.t())
    field(:status, String.t())
  end

  @spec new(user) :: __MODULE__.t()
  def new(
        %{
          "ingame_name" => ingame_name,
          "status" => status
        } = user
      )
      when is_binary(ingame_name) and is_binary(status),
      do: Utils.string_map_to_struct(user, __MODULE__)
end

An then OrderInfo is basically the same, as seen by this typedstruct definition:

  typedstruct enforce: true do
    @typedoc "Information about an order"

    field(:visible, boolean())
    field(:order_type, String.t())
    field(:platform, String.t())
    field(:platinum, non_neg_integer())
    field(:user, __MODULE__.User.t())
  end

Extra

One thing to mention here, is that struct will not convert string maps to structures, only atom maps. So in order to achieve my goal of converting string maps to structures, I created this little helper function:

defmodule AuctionHouse.Shared.Utils do
  @moduledoc """
  Set of functions used across the app, for utility purposes, like dealing with
  tuples, maps and other data structures.
  """

  alias Morphix

  @spec string_map_to_struct(data :: map, target_struct :: module | struct) ::
          target_struct :: struct
  def string_map_to_struct(data, target_struct) do
    data
    |> Morphix.atomorphiform!()
    |> data_to_struct(target_struct)
  end

  @spec data_to_struct(data :: Enumerable.t(), target_struct :: module | struct) ::
          target_struct :: struct
  def data_to_struct(data, target_struct), do: struct(target_struct, data)
end

Here I used Morphix to do the hard work, but this can also be achieved by other means, see:

Many thanks to all of the people who helped me get this far, from other communities as well:

• How to convert a typed definition to a typedstruct? - #5 by xpg - Questions / Help - Elixir Programming Language Forum
• types - How to convert a typed definition to a typedstruct? - Stack Overflow