So there are two kinds of microwaves:
- those that use sensor for popcorn (typically it is on top, there are some that use audio)
- those that have no sensor and just use a timer (those ask you how big is the popcorn bag)
You should use the popcorn button on the first ones, with the second type it is better to follow the instructions on the popcorn bag.
I think you need to look for a microwave with a moisture sensor
https://youtu.be/Limpr1L8Pss