React Native - Issue with ENV configurations in Android

The value that is passed to --variant option is basically a combination of product flavor and build type. By default there are 2 build types defined - debug and release. To add flavors like development, staging, production, define them below buildTypes in android/app/build.gradle -

    buildTypes {
        .....
    }

    flavorDimensions "default"
    productFlavors {
        production {}
        staging {}
        development {}
    }

Now with a configuration like this -

project.ext.envConfigFiles = [
    developmentdebug: ".env.development",
    developmentrelease: ".env.development",
    stagingdebug: ".env.staging",
    stagingrelease: ".env.staging",
    productiondebug: ".env.production",
    productionrelease: ".env.production",
]

apply from: project(':react-native-config').projectDir.getPath() + "/dotenv.gradle"

you can now build like you wanted -

npx react-native run-android --variant=stagingdebug
npx react-native run-android --variant=productionrelease

You can read more about Android build types and flavors here.
https://developer.android.com/studio/build/build-variants

For a similar configuration in iOS, follow this excellent tutorial.
https://www.bigbinary.com/books/learn-react-native/handling-environment-specific-configurations-in-react-native