I don't quite understand the leap from "No third party cookies" to "You need to create an account".
If you're visiting a site and they drop a cookie, that's a first party cookie. You don't need to log in for that to happen, and they can track you all the same. Taking identifiers from a first party cookie and passing them to advertisers will still be a thing, it'll just require closer coordination between the site and the advertiser than if the advertiser dropped their own cookie.
Now yes, that first party cookie won't follow you around to other websites and track your behavior there, but creating an account wouldn't enable this anyway. Besides, Google's Privacy Sandbox product suite is intended to fill this role in a less granular way (associating k-anonymized ids with advertising topics across websites).