@nprofile1q... I don't know if you are familiar with it, on top of a classic N64 controller, it has a closed slot, slightly smaller than with a memory pack, has rumble, and between L and R button 4 led, ZR button, home button and circle in square screenshot button.
Using steam test device inputs, some buttom make sense. Joystick map to left joystick, A, B, d-pad, L, R, start map to +, C-up and C-left map to X/Y
Other make less sense.
ZR map to L3. C-right map to -. C-down to right trigger, Z to left tri