In March 2021, Google announced its intention to start testing Federated Learning of Cohorts [FLoC]. According to Google, FLoC would be a replacement for third-party cookies that would allow browsers to enable interest-based advertising. Those tests have since been completed.
Web Dev says: Federated Learning of Cohorts [FLoC] provides a privacy-preserving mechanism for interest-based ad selection. As a user moves around the web, their browser uses the FLoC algorithm to work out its "interest cohort", which will be the same for thousands of browsers with a similar recent browsing history. The browser recalculates its cohort periodically, on the user's device, without sharing individual browsing data with the browser vendor or anyone else.
As of 2022, Google announced it was terminating Floc and replacing it with the TopicsAPI.