You have made your new app in the month of June for which facebook bidding is mandatory. So, integrate bidding to display ads in your app.
Q. Why older apps are displaying ads then?
Facebook has also given a deadline of 1st November 2021 for older apps to integrate bidding, After that, the ads will no longer be served on those apps too. For more information about these changes, you can visit your Facebook bidding dashboard.
Note that, Bidding is mandatory for all new and old apps so if you are making a new app or updating an older one, then use the Facebook ads adapter component to integrate bidding.