Curb Your Enthusiasm is not an Apple show. To see the shows available with your Apple TV+ subscription, choose AppleTV+ in the sidebar, then you will see the Apple TV+ shows.
When using the Home tab in the sidebar, you see content that is also available if you are a subscriber to any other service as well. For example if you also have a Hulu subscription, you can watch it in the Apple TV+ app without having to switch to another platform. You don't need to purchase that Hulu subscription through Apple to watch it there. The Home tab is also where you can rent or buy on-demand movies.
It is just like if you have Amazon Prime Video, you can watch HBO/Showtime shows on that platform, but you would have to have a HBO or Showtime subscription.