Hey @0llum,
As mentioned in the docs, the getSystemBrightnessAsync() method is experimental: https://docs.expo.io/versions/v28.0.0/sdk/brightness#expobrightnessgetsystembrightnessasync
Would you be able to create a feature request on our Canny: Feature Requests | Expo detailing exactly what you want to be able to get from the Brightness API?
Cheers,
Adam