There is no way that google has interest in the effort it would take to try to interpret the custom data that websites insert into custom analytics dimensions in a meaningful way. Their algorithms may track trends for them, but they are not aware of what they actually mean in a semantic way. I doubt that it us useful for them to learn anything from that data that is scoped outside the single account.
People are so confused about this. They underestimate the cost and effort that would be needed to just grovel around in GA logs and infer things, nevermind the fact that Google promises not to do it. Then the same commenters overestimate the expected value of successfully doing it, handwaving about how valuable it would be when in reality there is not a market for such data. Finally, they underestimate the risk it would pose to the adsense business, which prints more money than Jerome Powell, and the risk averse culture of Google who would not put that business in jeopardy for anything that pays less than a billion dollars per hour.
