What is the best way to store ultra sensitive data in app eg. Banking details of the user, credentials etc. The data should not be allowed to access by any other app even if user give some specific permissions to that app ( by mistake or knowingly).
Having the data on internal storage will suffice, if your “threat vector” is other apps accessing that data by accident. So,
getFilesDir(), SQLite databases in their default location, and
SharedPreferences all would qualify.
If your “threat vector” involves somebody else getting the device and attempting to extract the data, consider encrypted data stores (e.g., SQLCipher for Android).