I've attached screenshots below for your reference.
If you wish to apply the Credit memo when receiving a payment for an invoice, you can refer to the Step 2: Apply the credit memo section in this article for the detailed steps: Enter and apply credit memos and delayed credits in QuickBooks Online. It also contains information about the difference between Credit Memo and the Delayed Credit and how you can apply them to your transactions.
I understand how beneficial being able customize your Credit Memo transactions. We take this suggestion as a guide on which area of the product we should improve. I'll personally take note of this feedback about this feature for consideration in future updates.