VirtualHere with Wii U GameCube Adapter

Hello,
I am using the Nintendo Wii U GameCube Adapter (this one: https://www.amazon.de/Nintendo-GameCube-Controller-Adapter-Smash/dp/B00…) on my (Windows 10) PC. It is basically an adapter developed for the Wii U, so that GameCube controllers can be used on it.
But it features USB connections and is directly compatible with the Dolphin emulator (using the WinUSB driver) and works perfectly fine when I plug it in my PC and start a game with Dolphin.
(Here's some more information on the whole setup, if needed: https://wiki.dolphin-emu.org/index.php?title=How_to_use_the_Official_Ga…)

However, I want to use it on my Steam Link. So I purchased VirtualHere in the Steam store and started a Game on the emulator using Steam.
It does recognize inputs of some buttons (but e.g. the Start button does not work at all) and if I don't touch the controller, it will still somehow recognize inputs. Unfortunately, games are unplayable like this. I hope, you can come up with a solution.

Thanks in advance,
Marcel