Recently I interfaced with these 8x8 ToF ranging grid sensors.

Made me think I could try them out for a keyboard. I don't know maybe something obvious that would make it not work but could be cool to train an ML model.

There would also be a companion app that shows the real-time depth sensing.

These sensors have a 45 deg FOV so you'd need more than two... otherwise it'd have to be far away. Maybe 4. I did buy 5 so...

The FOV on these sensors is not  big.... so like I said you would have to have more than 2. Doing some modeling in sketchup with 1 sensor it has to be at least 8" away to cover my hand. Two of them maybe cuts that in half.