Sure, if they were giving your IP to a telCo who can map your IP to a name if you're a customer - that's identifying you.
It's HIGHLY unlikely this happened at the usual suspects (FAANG).
There are a bunch who basically pay apps to use their api and then take the data.
Apple was right to kill that imho. IIRC that was foursquare's pivot
There is also lot/lon in programmatic bid requests, but I don't think they're super accurate or granular and lots of fraud. (could be wrong, just from my small experience buy side using DSPs seeing lots of lat/lons being smack in the middle of a city)
[1] https://www.safegraph.com/guides/mobile-location-data-provid...
[2] https://developers.google.com/authorized-buyers/rtb/geotarge...
[3] https://fixad.tech/wp-content/uploads/2019/02/3-bid-request-...
They explicitly and unambiguously deny doing it; if that was incorrect, there would be a huge regulatory and public backlash. (Think of what happened with the Cambridge Analytica case, despite Facebook's hands being pretty clean on that). No disgruntled ex-employees blew the whistle on this but did on other issue), which suggests it probably didn't happen.
Selling ads is very profitable. Selling data directly risks that business for little gain. In addition to the backlash when that data selling were revealed, it risks somebody else using the data sold by Meta to outcompete them on ad targeting.
Companies typically don't admit to the public when they're engaged in unethical practices. Purdue Pharma is a good example.
Bingo. They're unlikely to be selling the data because those data are their secret sauce. They are as economically incentivized to build sociopathic models on you as they are to keep your data out of anyone else's hands.