Hello there, @Maple1.
It's nice to see you in the Community. I can help resolve the concern for the item notes on your invoices in QuickBooks Desktop.
I have replicated this using my test account, and it appears that Notes on your items won’t show or print on the invoices. However, you can add them to the Description field instead.
Once done, create an invoice. Make sure both Screen and Print for the Description column in layout designer is selected.
For more information about customizing forms, take a look at this article: Use and customize form templates.
That should get you pointed in the right direction. Reach out to me if you need anything else, I'm more than happy to help. Thanks for dropping by, and take care!