The "description" field seems to be labeled as "details" on the Mac. I use this for information about the job that I want to be seen by the client on the Invoice.
I have the "description" turned on, and I use it for details to be seen by the client.
The "note" field that I suggest would not show on the Invoice, it would be private for info that can be seen on my side, but never by the person receiving the Invoice.
If there is a way I'm not aware of to have certain private info visible to me, let me know. I would typically put in a note to myself like : "Pays by Zelle," or maybe "Pays by ACH to Chase," etc.