For example, Facebook offers you to pay to "increase the reach" of your posts. This happens for example when you try to post a message to a Facebook group. If you want to make sure all members see the message, you have to pay.
This is a way that Facebook monetizes without tracking (targeting is based on people who opted in to join a group) and the users pay directly in the app (allowing Apple to get their 30% for the in-app payment).
With Apples changes, Facebook (and others) might focus more on strategies like that.