You mean without the search engine knowing what you are blacklisting?

Perhaps there is no good way, but in the case of Google, it seems like it wouldn’t change the privacy equation to have this not be private from them.

No, I mean, in what way can this feature be implemented and avoid sharing any PII (assuming the list itself is not PII, since that list could potentially be the same used by other users)? What about a text file hosted somewhere, and the only identifiable information is the cookie containing the link to that file?

Are you looking for a way to avoid linking an individual user’s fingerprints with a blacklist?

Yes, or rather: avoid that the blacklist becomes an individual user's fingerprints. Appreciate any suggestions on how to approach that.