All good points, but they don't change the conclusion I wrote though, you effectively further specified the lengths to which Google is going to prevent any potential bad correlation to sensitive categories. Of course there will be correlation of some sort, they aren't random groups, but so long as you can't tell sensitive categories, you can only observe that a group seems more interested in a particular advertiser products. You can't tell their browsing history, just their interests.

Regarding the trial, yeah I know that origin thing is up, and the minutes for yesterday's W3C IWABG meeting aren't going to be out until next week, but the team working on this stuff at Google said that the trial up there is kind of fake and the code isn't merged in Chrome yet and won't be until 91, at some point I have to trust the engineers working on this stuff more than the rest.

[edit]: To be clear, I don't mean that there's no experiment going on, I just mean that it's not the browser running it, that the removal of 3rd party cookies as a way to opt-out likely is due to the fact that they may be relying on server-side computation to do this experiment rather than the browser, I wouldn't see why the browser would care about cookies to track your history, it's already stored in the browser.