Ender3 S1 Pro Motherboard - Full-auto input shaping (2ADXL)

Without a schematic it is quite trial and error. You can identify the potential pins from the F401 datasheet and trace back / measure where on the board these pins end up.

An alternative would be a Raspberry Pi Pico, which is a low cost alternative and quite comfortable to use. Basically a Pico should even be able to manage multiple ADXL on the same board as it has multiple SPI buses. See Raspberry Pi Pico + ADXL345: Portable resonance measurement