Hi there, @pmcdonald1.
Adding a custom field to the deposit screen is currently unavailable in QuickBooks Desktop (QBDT). In the meantime, you can utilize the MEMO column and enter the information you want to show on the report.
To learn about how custom fields work, see below articles:
I can see how this feature would be beneficial to you and other businesses. While we continue to make your experience with us even better, I encourage you to visit the What's New section on your QBDT account, to know updates with our latest news as well as product improvements.
If there's anything else you need help with, let me know by adding a comment. I'm more than happy to assist you. Have a great day!