In Super Mario Maker 2, a single Super World can contain a maximum of 40 courses. This capacity comes from the World Maker update, which lets creators arrange their courses into an overworld structured like a small, custom Super Mario game.
A Super World can contain up to eight separate worlds, and each world can hold up to five courses. Those five slots include a castle course, so the theoretical maximum is eight worlds multiplied by five courses: 40. Creators do not have to fill every slot, and a Super World may be much shorter.
The World Maker feature was added in the game’s third major free update on April 22, 2020. It expanded Super Mario Maker 2 beyond individual course creation by allowing connected maps, world themes, paths, fortresses, Toad Houses, and Warp Pipes. The overworld uses a Super Mario World-inspired presentation, although the courses inside it can use the game’s available styles, including Super Mario Bros. 3D World. “40 courses” is therefore the per-Super-World limit, not the total number of courses a player can create or upload.