Unfortunately there is no way to set a staff member to just have access to do the reconcile they would be able to still see the bank and other aspects of the product. You could leave feed back to our engineers and it might be something they bring out in the future.
I definitely see how you would want to have this user access limited to reconciling payments. Rest assured that I'll pass along your suggestion to our Product Developers. They're always looking for ideas to consider on how to improve QuickBooks Online (QBO).
In the meantime, I recommend visiting our Blog site to learn what new updates are being rolled out, as well as additional references while working with QuickBooks.
You can also visit these article to know more about managing user access in QBO: