Your screen shot makes things clear. Your CBA Business Account was created as a control account. That is, it summarizes subsidiary accounts. And, while you did not show the edit screen for the bank account itself, I suspect your CBA Business Account bank account is the only bank account assigned to this control account. That means it is assigned to itself.
From a functional standpoint, that is fine. But the Cash at bank control account cannot be disabled, because it is hard-coded into the program and becomes active whenever the Bank Accounts tab is enabled (as it must be to use a bank account). So you have two choices:
Leave things as they are, knowing that unless you assign another bank account to it, Cash at bank will always be empty.
Redesignate the control account for your bank account to Cash at bank and delete the custom control account you created named CBA Business Account.
If you do the second, you can then rename Cash at bank as CBA Business Account if you want by going to the Chart of Accounts page under Settings and editing that account. If you have only one bank account, this is what I would do. When doing this, you will be reminded of the name change because the default name will appear in gray on the Chart of Accounts page, but not anywhere else in the program.