It's the same technique of the "3D touch" the iPhone 6S had, though that was discontinued. Capacitive sensors measure microscopic changes in the glass, as it slightly flexes when you press it. Then a haptic motor does a little kick to simulate the feel of it being pressed down.

They've been doing this since 2015 or so. Prior Macs didn't click on the top 1/4 of the trackpad, because there was basically a "hinge" there and the glass would actually press on a physical button.

So there's a big big matrix of tiny tiny motors under the trackpad ?