As for your question, there is no point in trying to replicate results for the same query, search results and the displayed ads can wildly differ for the same query based on a large number of factors.
That's never been the definition. The fold is the bottom of the viewport on initial load, meaning nothing below the fold is viewable without scrolling. This is an analog to the fold in a newspaper, hiding anything below it.
It seems like most of the claims you've made in the this thread are false.
The issue here is that I’m talking about literally the line break between ads and regular results. There are multiple folds - search widgets, instant results, etc.
https://i.imgur.com/CFeWDY1.png
As for your question, there is no point in trying to replicate results for the same query, search results and the displayed ads can wildly differ for the same query based on a large number of factors.