reception All applications are sandboxed regardless of the source from which they originate, this is an integral part of the Android security model, and GrapheneOS enhances it.
Privacy and anonymity are not the same thing.
Use sandboxed google play in App Store for DL Briar,
As I'd never heard of this application, the only help I can provide is to use authorization toggles to the max, such as network revocation, sensors, storage/contact ranges etc.