We are still waiting for 16 circuits to Mario Kart 8 Deluxe by the end of 2023 as part of its Additional circuit passes. There Wave 5 has just been confirmed for this summer, on the occasion of a Nintendo Direct which highlighted some of the additional content it will bring.
So the DLCs will bring as always 8 additional circuits, and the first formalized is unpublished, and is called cleanliness race. As shown in the trailer, it will take the form of a giant bathroom with lots of animated objects. The novelties will not stop at the pitches, because after birdo for the Wave 4, 3 other characters will land via the Wave 5 : Flora Piranha, Wiggler And Kamek.
While waiting to discover the release date and the other 7 circuits, the entire Additional circuit passes can be acquired from €24.99 on Amazon.co.uk.