i have the same problem i solved it by change the platform target ios from ios 12 to ios 13 in podfile

ios > podfile platform :ios, '13.0'

and then remove the pod folder

and run this commands

• flutter clean
• flutter pub get
• cd ios // if using mac
• pod install --repo-update

the versions of package i using

• firebase_core: ^3.6.0
• firebase_remote_config: ^5.1.3