I updated the Ads SDK to 4.12.0 a few weeks and now Ads no longer work on a real Android device, also I can’t build an Xcode project for iOS
I’m not using Mediation, only Unity Ads, my code has always worked until I’ve updated the SDK
Is there a workaround, or are Unity devs working on this issue?
I’ve found a workaround by downgrading to SDK version 4.4.2
You have to remove the 4.12.0 SDK from Package Manager, quit Unity, and open the Manifest.json file
Add this line in the dependencies:
“com.unity.ads”: “4.4.2”,
Save the Manifest and open Unity again, you’ll find that SDK version and it will work like a charm
Hope this helps, anyway I hope Unity devs will fix this bug on a new version of the SDK 
I ran into the same problem.
When building with 4.12.0, the Frameworks/com.unity.ads folder isn’t added in the xcode project.
I’m also downgrading to 4.4.2 for now.