The documentations on Expo is crap confusing. I encountered the same situation like yours. The easiest way to fix is to use .easignore, simply copy all the contents from .gitignore except your google-services.json. The rationale is that EAS Build will ignore the file on .gitignore but at the same time you don't want to upload your credentials to Github. So by using .easignore, it will take precendence over .gitignore when it comes to EAS Build and it allows your google-services.json to be included in the build.

From my understanding, app.config is equivalent to app.json file, someone please correct me if i am wrong.

Hopefully this could help you.