This can be fixed using Zadig to install the proper driver, following the documentation from Dolphin Wiki (Just Google search 'how-use-official-gc-controller-adapter-wii-u Windows' without quotes, and go to the dolphin-emu website). While PC mode works fine on Windows 10, Wii U mode doesn't work out of the box. I've tried this adapter on both Linux (Kernel 5.4.34) and Windows 10, and while it works perfectly out of the box on Linux (Both PC mode, and Wii U mode with Dolphin), there's one small issue with it on Windows 10. Works flawlessly on Linux, and nearly flawlessly on Windows 10.
Feels cheap, but there's no input delay, and rumble works perfectly.
