Unfortunately the A21s does not have secure folder and there is no App lock functionality available. However you may backup your Notes on Samsung Clouds.
To Backup Data, please do the following:
On your phone, please do the following:
1. From the home screen, swipe either up or down to access apps. 2. Select Settings. 3. Select Cloud and Accounts 4. Tap on Backup and Restore 5. Select Backup data
