Earlier quoted context omitted.
In my anecdotal experience, FB is using non-logged in google search results to select which ad to show you. I assume google sells those to FB, based on IP address. But, my YouTube and Google search and ads, whole logged in, are based on what I do while logged in only. I might be naive but I have not seen correlation between my logged-in and my non-logged-in life within google products.
Another hypothesis: Silicon Valley is using your inner speech - obtained with electromagnetic surveillance and machine learning. People try to explain it away as Big Tech's blackbox AIs being good of making inferences from "public" data, but fail to consider that their body betrays their mind by leaking information under the skin, which can be picked up silently with microwaves.
Do you have any sources or information I can look up to study this?