Go to Mario Kart 8 Deluxe → Press + → Software Information → Version should say 3.0.3 . All Wave 6 courses should be unlocked in the Grand Prix menu.
If you've obtained an NSP or XCI file of Mario Kart 8 Deluxe and want to update it:
A new "Music" button on the top menu allows you to listen to game tracks, including DLC music even if you don't own the pass. Multiplayer Room IDs:
