I bet, if they haven't already, some of the info stored by sites is how we interact with it. And I bet with AI you can pretty much fingerprint someone based on habits.
So even your alt accounts will know it's you.
Edit: why do you think Reddit made the big push for their own app? Engagement, time spent looking at a post, how fast you scroll past something, all useful metrics for ad revenue. And we know that ad companies like tracking us.
Any spooky shit comes after the systems are developed for ads.