So there's leaks of information all over. Some love Facebook, and some find it creepy.
https://www.cnet.com/how-to/how-to-turn-off-this-creepy-facebook-feature/ notes TWO SETTINGS to change but as noted, it uses other than location data and once you gave up your location on any device, game over.
Here I ignore such things. As a programmer, I shrug a little at this.
My iPhone 5s Facebook app seems to have some preternatural power to cull info from every activity I perform on my iPhone. Example: it will suggest friends I have no friends in common with, who I only contact on a non integrated app. I don't have contacts synced, I don't have my phone number in Facebook, and I do not have location services enabled.