Olde time microwaves had a moisture sensor inside which allowed them to sense when popcorn was done popping, automatically. Really fancy ones have a microphone, and will listen for when the popping is done.

But lots of microwaves literally just throw on a popcorn button that's just some arbitrary preset time duration. These do not get consistent result, and as such, popcorn makers just tell people to not use the feature at all as they can't guarantee results.

In almost all microwaves, the control circuitry or mechanical switches only ever switch 2-3 power circuits: motor+fan(+bulb sometimes separately) and the heating (transformer+diode+capacitor+magnetron) high voltage circuit. It can therefore only switch the heat between 0 and max, usually in a slow (15-30s period) PWM cycle (that hopefully does not coincide with the tray rotation period). The inputs can be manual only, or sometimes there is also a scale, moisture sensor and microphone, along with thermal fuses for safety.

I think the pizza setting is just generic medium one with short 50% cycles to allow the heat to spread. The popcorn setting can be much more interesting:
https://www.youtube.com/watch?v=Limpr1L8Pss

Technology Connections on YouTube or a better alternative has done videos about the popcorn button at least.

Fwiw I've never ever seen settings like that. Maybe it's only for American market?