Hello mikepAngola,
Thanks for taking the time to explain what you've done so far to set up the custom fields on a list item. It sounds like you know your way around the program and I want to make sure we have the answers you need for figuring this out.
In QuickBooks Desktop, certain features and configurations must be handled in single-user mode, as you've discovered with setting up custom fields in for your list items. Since you're not able to see the options when you switch into multi-user mode, it may be a product limitation. But there are a few other things I'd like to have looked at before we jump to that conclusion, just to be sure.
For that, I recommend reaching out to the interim QuickBooks Desktop chat support team at http://intuit.me/cachat. QuickBooks Desktop is primarily a phone based support system, however due to COVID-19, we've had to reduce staffing and put a chat option in it's stead for now. Don't worry, we have the same solid agent team backing you and ready to help. Someone will be able to work with you to make sure everything is configured as it should be and then determine whether there's something missing or this is a product limitation.
Don't be afraid to reach out! Feel free to familiarize yourself with the Intuit QuickBooks Desktop software support policies so you know what to expect when you reach out.
Have a great weekend!