Okay, but: a) is blocked by site partitioning, b) doesn't have per-user tracking information, and c) only works (of course) if you've explicitly signed in with Google on that site. I don't think Google supports third-party tracking for ads via that personalization path yet, but plenty of non-Google advertisers do: they take your hashed email address and use that to replace their third-party tracking cookies. This is what the ad community is hailing as their "privacy first" approach that breaks Google's "monopoly"—sending your email address to every single advertiser who they partner with.