IAP is planned to be integrated in the engine, but can't say when. Maybe 3.0, or 3.1. Devs are still discussing how to design the generic "game store"/"social" API for using In-App-Purchases.
Ads were also being discussed a bit at GodotCon (along a list of features the engine still needs, because 3.0 is a great opportunity to break compatibility and make a big step forward), but I have no idea when it will be scheduled for development. At the moment I only know of some stuff for Android (quick search gives this https://github.com/Mavhod/GodotAdmob) but it looks outdated.