I'm pretty sure they can use the meta data the pull from your various interactions with search and the text you post online. These services build fingerprints of your habits using these techniques to follow you everywhere. At some point in the chain they could easily connect this fingerprint to your identity as soon as you log into and account that contains a piece of identifying information about you. The threat is real. I can foresee someone programming a terminal or app that obfuscates online behavior to avoid this fingerprinting in the future.

Unless I am misreading something. Take a look at surveillance capitalism to see what's possible right now. It's going to be 100x worse as LLMs become more advanced.

It's not the things you post online, it's the nuances behind the way you type and other ways to determine behavior that allows them to be able to build these kinds of profiles.