The Placebo button

Wikipedia:

A placebo button is a push-button that appears to do something, but actually has no effect, like a placebo. In other cases a control like a thermostat may not be connected.

Many walk buttons at pedestrian crossings in New York City were once functional, but now serve as placebo buttons.

Some door-close buttons in elevators are placebo buttons, although some of them do in fact change the timing, and others are only functional when activated with a maintenance key.

Some office thermostats may also function similarly.