FLoC is Google's loophole after disabling third-party cookies in Chrome and promising they "will not build alternate identifiers to track individuals as they browse across the web"[0]. FLoC is a new tracker to replace third-party cookies, but it works by putting users in groups and tracking those groups, so they technically aren't tracking "individuals" this time. Except you can use FLoC to track individuals by identifying them as a unique intersection of many disparate groups[1].
[0] https://www.theverge.com/2021/3/3/22310332/google-privacy-re...