Can't enable Hermes on iOS


I have a project where I can’t turn Hermes on for iOS.
In my app.json I have :
"jsEngine": "hermes"

But still when I do “expo prebuild --clean”, delete all derived files and clean project on Xcode I can see that I’m not using hermes after logging the following command :

  const isHermes = () => !!global.HermesInternal;

I’ve also tried to make an EAS build and the function still return false.

Expo SDK: ~46.0.19

Edit : The method HermesInternal doesn’t seem to exist.
Still when I try to debug with flipper and going to hermes debugger, it says “Metro is connected but no Hermes app were found”.
When trying to open the debuger with “j” I got : “No compatible apps connected. This feature is only available for apps using the Hermes runtime.”.
How can I be sure that I use Hermes ?

Any idea ?

So for anyone who has the same problem, it was the "use framework : static" that was used in combination with rnfirebase that was causing the problem.
I updated to expo SDK 47 which updated the react native version and now It’s working properly.