Generic debugging steps
Test with evtest
You can test if the touchscreen emits any events with
Test with libinput debug-events
You can check if libinput understands the events your touchscreen driver emits with
For example it's possible that libinput doesn't get any events or that it doesn't get TOUCH_DOWN/TOUCH_UP events. You can see the raw events libinput receives with
Some touchscreen drivers on Mediatek devices have issues because they don't follow the standards. You can compare the driver source of your driver (especially the functions
tpd_down) with the Fairphone 1 touchscreen driver and see if adjusting your touchscreen driver to mostly match that behavior helps.