The latest Nintendo Switch update, 4.0.0, secretly added support for the GameCube controller.
In order to use the GameCube controller, which is arguably one of the best video game controllers ever made, you’ll need the Wii U GameCube adapter (seen below), which connects the controller to a hub, which connects to the console via a USB port.
If you’re interested in playing Switch games with a GameCube controller, there are a bunch of third party adapters. Like this highly-rated one on Amazon for just 25 bucks.
