Unity editor version: 2019.3b6
Firebase Unity SDK version: 6.6.0
Firebase plugins in use (Auth, Database, etc.): Analytics, Crashlytics
Additional SDKs you are using (Facebook, AdMob, etc.): Admob
Platform you are using the Unity editor on (Mac, Windows, or Linux): Mac
Platform you are targeting (iOS, Android, and/or desktop): iOS

(Please list the full steps to reproduce the issue. Include device logs, Unity logs, and stack traces if available.)
The post build process crashes with a deprecated Unity - iPhone message

What's the issue repro rate? (eg 100%, 1/5 etc) 100%

Stacktrace: