Number_8363 The GrapheneOS camera has been intentionally made so that it cannot be disabled because the system uses it even if you don't directly.
Apps using system capture intents (using the system camera rather than their own implementation) can only do so using the system camera, not another third-party camera app you've installed. Leave it enabled, and you're free to use another camera app as your standalone app. The system camera app is still needed, however.