So Nintendont was updated to support the GC adapter for Wii U

Gbros

For Gamecube Adapter Switch Gamecube Controller Adapter Wii U PC and Switch, for Super Smash Bros Choice Adapter Game Cube Plug and Play

Gbros

GC Controller Adapter for Wii/Wii U ( Edition) for Nintendo Wii, Wii U

GameCube Controller Adapter for Wii U, Nintendo Switch and PC USB – Lexuma

Nintendont and my wavebird aren't working on my Wii U and need help

4 Port GameCube Controller Adapter for Nintendo Switch Wii U PC Super Smash Bros

Finally. Ive Been Waiting For YEARS : r/WiiUHacks

Connect two GC controllers to a Wii or Wii U system. Built in Turbo. Compatible with all games supported by the Wii Classic Controller, Wii Classic

Mayflash GC Controller Adapter for Wii & Wii U (Dual Pack), White

Mayflash GC Controller Adapter for Wii & Wii U (Dual Pack), White : Video Games