All this focus on cookies and FLoC feels like smoke and mirrors from Google.
Modern adtech can track users regardless if cookies are enabled or not, and whether they enable this new Chrome feature or not, via browser fingerprinting. They've been doing this for years.
So this new "privacy sandbox" is a diversion to the public, and particularly to law makers, that signals "see, we care about user privacy". When in fact it ultimately makes no impact on their revenue.
The public and law makers are barely starting to get an understanding about cookies, and there's a growing concern about them, so this is Google being proactive towards the blowback. Fingerprinting is much more complex to understand, and concern about it is so under the radar, that it will take many more years for the focus to catch up to these nefarious practices.
The frog is being boiled[1], make no mistake about that.
One of the explicit goal of "privacy sandbox" is preventing browser fingerprinting by limiting informational entropy from user environment. https://github.com/mikewest/privacy-budget