What normally happens is that an app can see what you’re up to. It can see what you are looking at inside the app; for example, in Facebook what groups you belong to, who you regularly interact with and so on. This continual monitoring allows the app to personalise your experience. In a nutshell this means that the ads that appear on your screen are targeted just for you and reflect your interests.
With the IOS14 update, the Apple user will see a pop-up message appear asking them to allow the app to track their data. This will be for ALL apps. The user decides whether to agree or not.
It’s anticipated that around 60% of Apple iPhone and iPad users will say no and not permit apps to monitor their activity and track their behaviour. This IOS14 impact on Facebook Ads is already significant. When the rollout of the change is complete, those users who say no will lose their personalised experience in the apps on their devices and will be seeing more adverts that I’m guessing won’t be of interest.