It is true that slots are not completely random since computer science has not yet come up with a way of creating a true random number generator. This means that the spin’s final outcome is decided the moment you press the spin button, and stopping the reels or doing anything else will not change it from that point on.
The fact is that all slots, even the older generation ones, are equipped with an RNG (random number generator) chip, which generates numbers within a massive spectrum and decides on the outcome of a particular spin.
It is a widely accepted assumption, especially in live casinos, that slots that are loaded with money from one or several players will eventually pay it out to another. There are many theories floating out there, but most of them are completely wrong. Before you can know how to win at slot, you need to understand how these games work in the first place.