So the whole point is you don't have IDFA, but each app still has its own persistent ID. Before when you used the FB app and another app they both got same IDFA

So the whole point is you don't have IDFA, but each app still has its own persistent ID. Before when you used the FB app and another app they both got same IDFA so FB could link them (the FB SDK in the other app posts the IDFA). However, even with Apple change, the apps can still make network connections. All FB needs to do is make its SDK ping a server with the app specific ID and correlate with IP addresses. FB app sends IDFA1 with IP1 and MyAPP sends IDFA2 with IP1, they both have same IP therefore IDFA2 is the same user as IDFA1. Statistically you can get 95%+ matching very quickly. If you never use a wifi and are always on the same mobile network in the same city, then FB cannot distinguish you from other people who never use Wifi and are on the same city as you, but even then, the mobile phone network traffic has 10+ external IP-s so a few days of traffic will correlate quickly. Even worse, when before FB could get away without beacons in the SDK, just sent IDFA once and then just request ads, no need to store IP address every 10 minutes. Now it needs to ping every 10min to get the correlations. Apples next step is then a universal VPN/Proxy that all apps need to use so all traffic goes through Apple servers in the name of privacy. Then FB would see the same IP address on all requests, until that happens though, this is just a smokescreen.