tvs diode for push button switch section
The TVS is there to catch high voltage peaks that can occur when YOU  touch the button.

There is no high voltage source in the circuit that could produce high voltage.

The human body is, however, a fairly decent high voltage generator.  You can easily build up a potential of several thousand volts just by walking on a dry day.

If your body is charged up, then you can cause damage to the circuit by touching the button.



Actual damage is fairly rare.  Many circuits don't bother with a TVS or other over voltage protection.

Whether you need it or not depends on a lot of things.

Is this a hobby project?  Well, odds are you don't need the TVS.

Is this part of a control circuit for a medical device that could kill someone if it misbehaves?  Probably best include the TVS (and many other things that are required for medical safety.)

There are millions (billions? trillions?) of electronic toys that don't have over voltage protection.  We don't have a huge flood of devices dying every day from getting zapped by their users, so the odds are pretty much against it being a problem.