Delivery / returns track the physical product, while invoice/ credit notes track monies.

>> I created a credit note from the invoice but do I need to return the order from delivery? <<

The answer is specific to your situation, if you wish to keep track of the products as well, then you would create an inventory move.

a. Return if the product was returned to inventory
b. Scrap if they product was scrapped
c. If product is retained by customer and only refund provided then you wouldn't create any inventory move.

The effective way would be to track product as it keeps the SO updated and credit notes or invoices can be created directly from SO.

Hello, 

- Credit Note is for financial (returning money)

- Return is for inventory (returning products back to stock)

Hope this helps

Hi,

Credit note

A credit note is sent when a customer returns merchandise to the supplier or seller of those goods. However, credit notes are usually used in the commercial world after things have been returned.

Return

Product return is the process of returning a product that was previously purchased by a customer, and in turn, receiving the refund in the form of original payment. Moreover in Odoo, a customer can return the purchased product even if it is paid or not yet paid. There are several reasons to return a product such as the product doesn’t match its description, the product is no longer needed, the product was damaged upon its arrival, and many more based on the situation and the desire of the customer.

for more details.Please refer the link

https://www.cybrosys.com/blog/use-of-credit-notes-debit-notes-in-odoo-15

Hope it helps