What spot are you trying to jump from? Bc there shouldn't be any invisible walls on either side of any of the mushrooms or the platforms. The area is designed for exploration, so if you haven't figured it out by now, it must be a bug. There should be a cave wall on the left of the mushroom platforms, near the treasure chest, that makes it obvious you can't go that way. But the rightmost mushroom shouldn't have anything beside it, and you should be able to jump and then dash midair to the platform.