Not 100% sure it was Amazon, but a month or two ago I actually got a physical junk mail letter after looking up a brand of dog treat online. (I don't have a dog, it was a random question I had about it.). I'm surprised it doesn't happen more often. You have to expect that nowadays every time you get online there's basically an AI sitting on the other side taking notes.
Amazon uses your Amazon history to target Amazon ads to your interests. That's not the same thing as giving your Amazon account information to a third party.