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

GameCube Broadband Adapter (BBA) support is now implemented in Nintendont. You can use either a USB LAN adapter or your Wi-Fi. : r/WiiHacks

How to use a Wii as a GameCube - Quora

So Nintendont was updated to support the GC adapter for Wii U. This is now possible. : r/wiiu

Smash Bros. Brawl can now support the GameCube Adapter on Wii U : r/smashbros

Wireless GC controller options for Nintendont? - The Independent Video Game Community

Gamecube Controller Adapter Switch Gamecube Controller Adapter Wii U - 4 Ports Game - Aliexpress

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

USB Replica Nintendo Gamecube Controller On Nintendont

Third party Gamecube controller adapters for Nintendont.

Nintendont Wii U 2022 Tutorial / GameCube On Wii U