Google has created FLOC as a way to work around the third-party cookie ban by browsers, which basically kills their ability to track users effectively.

Thankfully, they're playing "nice" as they want to scale adoption of this, and thus allow sites to opt their users out.

That is done by adding a

Permissions-Policy: interest-cohort=()

to all of our HTTP responses.
see https://wicg.github.io/floc/#permissions-policy-integration (of course the default is allow anything).