GameCube controller is compatible with Nintendo Switch now, still need an adapter, but they work.
In the console’s latest system update, support for the old controllers was added with no announcement. It still needs the Wii U controller adapter — no longer made by Nintendo but still found new or used at most retailers.
Users of the old GameCube controllers know that they don’t match up exactly to the configuration of the Nintendo Switch. There’s no home button, for example, so it’ll require some swapping to get back to the main menu from within a game. But for those who developed skill and muscle memory on the OG controllers, particularly for fighting games, it’s a decent option to have.
Update 4.0 has rolled out, adding video capture for certain games and the ability to transfer user profiles and save data to a new console.