In PentoWeb.RatingLive.Index.product_rating/1 function, there is a call to <RatingLive.Show.stars rating={rating} product={@product} />. Later on, the function is referenced as having the only argument:

with the yet-to- be-built Show.stars/1 component…

what is in line with the defined later function:

defmodule PentoWeb.RatingLive.Show do
  use Phoenix.Component
  use Phoenix.HTML

  attr :rating, :any, required: true

  def stars(assigns) do
    ~H"""
    <div>
      <%= @rating.stars
      |> filled_stars()
      |> Enum.concat(unfilled_stars(@rating.stars))
      |> Enum.join(" ")
      |> raw() %>
    </div>
    """
  end
...

VS Code even displays a warning about it.
Later, on page 224, the call is correct though:

<Show.stars rating={rating} />

One more point regarding defining an alias for alias PentoWeb.RatingLive.Show on page 224:

Make sure to alias the module in survey_live.ex like this
PentoWeb.RatingLive.

First, the name of the module is not wrong (survey_live.ex) and should rather be RatingLive.Index. In this case, as alias PentoWeb.RatingLive being already aliased (defined on page 218), the correct module to be aliased would be alias PentoWeb.RatingLive.Show, and alias PentoWeb.RatingLive should be removed.