SnapChat does the same thing, we (not me technically, I am just a developer that worked with our ad team) set up Geofences around events to serve ads and we could continue to target those users for continuous remarketing as soon as they stepped foot into and out of a location of our choosing. In our case it was mostly a concert and car race. We knew -a lot- more than we probably should have. You could push filters, and all kinds of stuff within those custom geofences. Facebook & Google have similar, but it's not near as granular as what I saw with Snap. They might have changed it by now, this is when they first were getting into advertising. It honestly wasn't very effective, probably because of the demographic that uses SnapChat.

Tiktok was used to find and track/monitor Chinese dissident whereabouts a few years ago by the CCP in Hong Kong.