How can I enable the Hermes engine in react-native

I followed the official docs to enable the Hermes engine in my app but the following always returns false:

    const isHermes = () => !!global.HermesInternal;
    console.log('>>>>>>>>>>>>>', isHermes());

The changes I made are setting the following in android/app/build.gradle:

project.ext.react = [
    enableHermes: true,  // clean and rebuild if changing
]

Then I did a clean build with:

cd android && ./gradlew clean

yarn android

But the console.log always returns false