Header file (FirebaseCore/FirebaseCore.h) not found, despite importing Firebase.framework

Make sure you are opening the .xcworkspace file instead of the .xcodeproj file.

I was troubleshooting for at least an hour before I determined this was my mistake, so hopefully this answer will save you some time!

Please check on edit scheme -> build -> check if Find implicit Dependencies is enable. if no, enable it and rebuild.

Try remove the Podfile.lock file and Pods folder.

Run pod install.

This worked for me.