Flap Clash uses Firebase authentication for user login. The preferred sign in is Google Play Games or Apple Game Center. When signing in with those, the app developers can only see the Play Games or Game Center ID. When signing in with email and password, the credentials are secured by Firebase and the developers can only see emails. To delete an email or ID from the record, request so here.
The only other user data is the display name the user can set. All other data collected for Flap Clash is related to the game play and nothing else. It is tied to an anonymous user ID.
Flap Clash uses Google Crashlytics to help developers fix bugs, the data captured is anonymous.