I took a WaveShare RP2040-Touch-LCD-1.28and made a program to use it as a touchscreen. This is still very much in the beta phase but the proof of concept works. Here’s my GitHub repo for it.
I’m planning on integrating it into my next split near the thumb cluster.
Oh neat! QMK seems to be the most appropriate for trackpads. I was thinking of something that could be wireless which afaik QMK doesn't support. And ZMK's support for pointer devices is not great just yet.