tl;dr: Set your controller and/or wireless adapter to
X mode or
X input. That is the hidden trick that gets Tesla to recognize the controllers as if they were Microsoft/XBox kind of controllers.
I just upgrade my 2016 Model X 90D to MCU2 as well, and managed to get the
8Bitdo SN30 Pro+ controller to work both wired and wirelessly (with the
8Bitdo USB Adapter).
For wired, I had to start the controller in "
X-Mode" which is also the Windows mode (
Manual). This is when you turn the controller on with Start+X both held until the light turns on. For the Pro+, the bottom LEDs light up the left two LEDs letting you know it is in this mode.
For wireless, I had to update my 8Bitdo USB Adapter to v1.33, specifically for the SN30 Pro+. Then, you only need to do this once, you need to switch the 8Bitdo USB Adapter to "
X-Input" which I assume is the same as Windows mode (
Manual). This is done by having your wireless controller already paired with the 8Bitdo USB Adapter, and pressing and holding SELECT and UP for 3 seconds. The adapter will blink like 3 times and restart itself. At this point, unless you do another hold select + a direction arrow for 3 seconds, you should never need to do this again.
Now, my 8Bitdo SN30 Pro+ will pair with my 8Bitdo USB Adapter, and I can do Beach Buggy Racing and Cuphead. Before these little X-mode/input tricks I couldn't do any of the new games, only the old ones.