Arthur backup is used by its owner only. It asks Google for access to just the files it creates itself in the owner's Google Drive (scope drive.file); it cannot see any other file.
The backups are encrypted before they are uploaded and stay in the owner's own Google Drive. No data is sent anywhere else, shared with anyone, sold, or used for any other purpose. Arthur backup keeps no user data of its own besides the login token it needs to write those files.
Use of information received from Google APIs adheres to the Google API Services User Data Policy, including the Limited Use requirements.