It isn't as easy as it sounds. It's a lot of fingerprinting, location, and metadata aggregation from an astounding variety of sources that is extremely difficult to fake - It can pinpoint you to an astounding degree. I have been working off and on the last 3 years in the privacy space (passion project) on a similar concept of adtech data obfuscation, and it's far more complex than just "put a fake birthday in a form" (although stuff like this can manifest in interesting ways).
Differential analysis is amazingly powerful. If you're in the US - 30 bits is all you need. And not all bits are equal - some come with implicit anchors, allowing you to segment and search efficiently.
If you know the state, the median number of bits needed is 23. If you know the city, around 10 bits is all you need to identify you as a unique individual.
A drunk raccoon with one eye and a missing paw can sieve out 10 bits of information about a particular person.
You can do probabilistic assumptions and segment the population by fuzzy characteristics you get, like stylometry, assumptions about native language, interests, etc. For a giant database like the spies and agencies have, they can do probablistic ID with extreme accuracy based on a tiny number of leaked bits.
If you snag a giant pile of readily available website data, then tag the person of interest based on that data, then any time you process new data, you can get a probability of that new data being associated with an already known person. Set a five nines threshold, or higher, and then assume those matches are legitimate, and you can chip away at all sorts of identity handles. From there, you can start doing contrastive searches, sieving out known quantities, improving the statistical accuracy of those fuzzy parameters.
Deanonymization and such is borderline trivial, consumer compute is about 5 generations past the threshold where a global database would be considered particularly difficult or challenging.
Fingerprinting is very easy, but obfuscating it is incredibly challenging, with all of the implicit, deliberately leaky data transactions that are imposed on us.
Would you ever blog/talk about it? Sounds interesting.
"Phone Swap Collective" ... You keep an extra smart phone... then just swap phones with people who commute to different areas of your city each day. Keep social media accounts that are effectively "bots" on the collective and post real BS multiple times a day via AI bot interactions.
Give a prepaid to homeless along with a month long bus pass... let 'em ride all over town.