Currently on Android the caller of Fingerprint.authenticateAsync is responsible for showing a message/prompt/modal to the user.
A minimum-viable implementation like in iOS is not trivial. It should have a "cancel" button that, if tapped, rejects the Fingerprint promise.
It would be great to have a minimal screen, similar to the iOS one, provided directly via Expo.
One way could be to expose a Fingerprint.promptAuthenticateAsync that, in Android, shows the default prompt. This way the code would be also a useful example for whoever needs to personalize this screen.