The Add option under the Action column shows when there is no transaction created in QuickBooks Online (QBO). Thus, the Add option allows you to record the new transaction in the register.
You can check out these articles that can give some insight into reconciling process:
Hope you’re doing great. I wanted to see how everything is going about the add option mean on the banking that you had the other day. Was it resolved? Do you need any additional help or clarification? If you do, just let me know. I’d be happy to help you at any time.
Looking forward to your reply. Have a pleasant day ahead.