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

Freeze when using GCN controller adapter with WiiU injects · Issue #712 · FIX94/Nintendont · GitHub

Connect upto 4 classic gamecube controllers to a Wii U or PC USB or switch Game with the classic gamecube controllers

GameCube Controller Adapter for Wii U, PC USB & Switch - NEXiLUX

Can you use the gamecube adapter for wii games that support gc, like mario kart wii? : r/wiiu

New 2020] How to use Official GC adapter on GC Emulator for WiiU! (nintendon't)

Gbros

Nintendont Controller-Configurations, Page 4

gamecube Controller Adapter (For Switch/WiiU/PC) – YCCTEAM

Gbros

GameCube controllers now compatible with Switch via Mayflash GC Adapter!