It’s absolutely true. It is a documented fact. It was discovered and entered into public record during the DOJ antitrust investigation into Google Chrome.

They call the signal „popularity“ and it is a successor of the Google Toolbar signal.

https://www.justice.gov/opa/pr/department-justice-wins-signi...

This is why Chrome begs you to login constantly and will do it automatically when you login to Gmail through Chrome. Everything you do in the browser (bookmarks, settings, address bar) is data about you sent to Adsense. No need for cookies when you control the browser and know who is using it.

Edit: also private browsing isn’t exactly private when you’re logged in to the browser.

Something worth inspecting further. We know that Chrome stores and sends the browsing history but this is an interesting vector.

There's no reason to think it isn't true. It matches every pattern of behavior observed from every tech company.

Chrome sends home the urls you visit together with the page performance data (and probably more). That's how they build Chrome User Experience Report (CrUX) for the most popular sites: https://developer.chrome.com/docs/crux