Credit notes in Quickfile are a confusing mess as I have noted and also the adding random bank entries should really be fixed by now. However, as these are the way they are you need to either write down how you do it or tear your hair out every time as there isn’t a nice simple way to do credit notes.
To do it without creating random bank entries I do it thusly. First create a credit note (which is often attached to a random invoice as you can’t just simply throw a credit note in the list) then create a negative value purchase in the receipt hub (credit notes are all uploaded with invoices as you would expect) and then tag this to the credit note you have just created. Involves some backwards and forwards as you can’t just create one on the fly, as you have discovered.