The idea behind Google FLoC is that advertisers will still be able to send you targeted ads even though your personal identity will be “lost in the crowd” of users with the same cohort ID. However, there are still many privacy issues with this approach.
Browser fingerprinting. By narrowing down your cohort ID, it’s possible to personally identify you by gathering data about your Chrome plugins, extensions, preferences, and settings, along with your IP address.
Discriminatory advertising. Google claims that FLoC will filter out websites and searches that pertain to things like race, sexuality, and religion so that advertisers aren’t able to discriminate when choosing which ads to display. But Google has repeatedly failed to prevent discriminatory advertising in the past, and there’s nothing in the FLoC whitepaper that suggests this will change.
False sense of security. While FLoC makes it harder for third-party advertisers to personally identify you, this still doesn’t prevent Google from collecting personal data on Google Search, YouTube, or any other Google service. Furthermore, Google will be constantly monitoring data and sorting users into cohorts, allowing Google to continue having access to a lot of personal data.