Best Buy has sold out of both the standalone console and the Mario Kart World bundle. The Nintendo Switch 2 has been difficult to find in stock since its June 5

You can't simply go to the My Nintendo Store and buy the Switch 2. To order the Switch 2, you need to log in with an active, paid Nintendo Switch Online account. Once you do that, you can choose either a Switch 2 standalone console or the Mario Kart World bundle and then hit the confirm button to "register your interest" in ordering a Switch 2.