The Membrane switch is similar to many devices with touch membranes.
Bottom is the Copper PCB or Copper foil or Alum foil or Film with conductive (carbon/graphite/etc) circuit.
Center is cardboard with Hole/Gap
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There are a few Touch-Screen examples in the Arduino Example's menu but, I've never used them.
I've made several Touch buttons similar to those purchased - that's easy to do in Kicad (and other PCB design software)...