I don't really understand this mindset. Google controls Chrome. They openly track every page you visit and show it to you at https://myactivity.google.com/ .
It's possible that Google is tracking you with FLoC or with extra HTTP headers or whatever. But they're also openly tracking you all the time anyway because you use Chrome. If you don't trust them to use the data they collect responsibly, don't use Chrome. (I'm not saying you shouldn't pressure Chrome to collect less data, I'm saying it doesn't make any sense to theorize about secret HTTP header fingerprinting operations when they're making literally no effort to hide the much bigger data collection operation right in front of you.)
My guess is they are still tracking you. Kind of like how fb creates shadow profiles for people who don't have an account. So they do all the same tracking, you just don't get to see it in a nice dashboard!
It's possible that Google is tracking you with FLoC or with extra HTTP headers or whatever. But they're also openly tracking you all the time anyway because you use Chrome. If you don't trust them to use the data they collect responsibly, don't use Chrome. (I'm not saying you shouldn't pressure Chrome to collect less data, I'm saying it doesn't make any sense to theorize about secret HTTP header fingerprinting operations when they're making literally no effort to hide the much bigger data collection operation right in front of you.)