whitcortex-backup is a personal backup tool. Only its owner uses it. It isn't distributed, and it offers no service to the public.
It stores encrypted backup copies of the owner's files in the owner's own Google Drive.
It requests a single Google permission, https://www.googleapis.com/auth/drive.file. That scope limits it to files the app creates itself, or that the owner explicitly opens with it or shares with it. The app has no file picker, so in practice it works only with the files it created. It cannot browse, read or change anything else in the account.