All of the Touch logic is embedded into the screen so realistically, touch issues are usually screen related. Otherwise, look for connector damage on the logic board. You could also probe the connector in diode mode and compare to a known-good device (or a tool like ZXW). The XS Max has fundamentally the same design as the X so you could use the X schematic for your troubleshooting. I would focus on the touch related power rails to insure they are not shorted.