Nintendo Switch’s 4.0.0 update is the gift that keeps on secretly giving. After it was discovered that wireless headsets were now supported, another secret feature has been found thanks to MasterMewKing on Twitter. Wii U Gamecube Controller Adapters, which became available back in 2014 for Wii U, now work with the Nintendo Switch.
This means that anybody with with the Adapter and a Gamecube controller can use the controller on most Nintendo Switch games after connecting it to the dock. Although, there may be some functions missing, as the Gamecube controller is missing the ZL button function and a Home Menu button.