It will be launching in Winter 2023.
When Nintendo announced the Booster Course Pass for Mario Kart 8 Deluxe, they revealed that we would get six waves with two cups each (a total of eight tracks) over the course of two years. During the Nintendo Direct, we finally got a proper look of things to come in the final Wave 6, which unfortunately didn’t get a release date others than « Winter 2023 ».