Please excuse my ignorance here, but how do we know that?
We also have whistleblower data that they (allegedly intentionally) intentionally ignored manipulation for the 2016 election. Worth reading Sophie Zhang's narrative:
https://www.technologyreview.com/2021/07/29/1030260/facebook...
Sure, none of these is a smoking gun for the explicit claim that the companies themselves are explicitly manipulating users, but they certainly appear to be complicit. Complicit in a conspiracy (in the legal sense) to influence voters.
Someone else did post some material though, and I was able to find some information googling myself as well.