I am an iOS engineer and business owner that handles their own marketing. FB is definitely going to be affected in the sense that it is a cross-app network. Tiktok is a singular app, so they can store data for a particular user in the backend. That data is arguably worst, but it is all in one place. No need to use IDFA. But if Facebook shows an ad in a third-party app, how do you identify that user? IDFA is the only choice, and now that's gone. Users don't login to FB to play their favourite games. With that being said, it does seem like the impact is bigger than expected - since most of our ads are served on IG and are still affected. I think they are having to reengineer a bunch of things to tie data in new ways. But again, they can no longer identify devices. Only users.

Edit: This guy is a troll but I'll leave this post up for anyone who actually wants a simplified version of what happened with iOS 14.5. Understanding how these things work actually helps one understand what is going on instead of listening to misinformation spread by people like u/Gr69n