The PlayStation controller PCB uses conductive pads that short to ground when the buttons are pressed. Using a continuity tester, I diagrammed these traces and the copper test points we will use to wire the buttons to the microcontroller.

You can see from the above diagrams that we'll wire up most of the PlayStation controller buttons to GPIO pins on the ItsyBitsy ESP32. The R2 trigger button will be wired to the Reset button, and the L2 is left unused. (You could chose to wire it and adjust the Arduino sketch if you like.)