From now on we need to set the Request IDFA into our apps to get approved for App store for iOS. I uploaded a build without it, and got rejected twice. (They asked me where they could see it). But then I put it in, and I got approved directly. I still have not really found the best "placement" in the game to show it yet. So for now, I just show it on startup on the menu screen. (You can place the event wherever you want, but you need to show this IDFA before the user see any ad, otherwise the app will be rejected in the review! If you don't show it on "startup" you will maybe need to write a description to the review team on the review notes for them to find it)
The IDFA will only be shown once to the user, where they can click allow/disallow. Then it will never be shown again, but can be changed in the app settings on the iphone, a setting called "tracking". (The IDFA window is shown in the local phone os language!)
If the user press Allow in the IDFA window then the consent is passed to Admob and they will serve "localized" content (higher ecpm) ads, if the user press disallow then Admob will serve "unlocalized" content (lower ecpm).
This setting is not related the the GDPR consent window, which still needs to be verified to EU citizens. So unfortunately those users will now need to get two ugly consent windows which doesn't really give a good impression when starting a new game.. but this is the new rules