Hello there, @lessenberry-anim.

Let me share some information on how the custom field works in QuickBooks.

When setting up a drop-down list custom field, you can add up to 100 options or items. Once you used-up all the available drop-downs, the Add item link will no longer be clickable. 

You can read through this article for more detailed information: Create and edit custom fields in QuickBooks Online Advanced.

Also, I've added these articles to help you manage your custom fields:

• Filter, search, and sort with custom fields
• Use custom fields in reports in QuickBooks Online Advanced

Swing by here if you have other questions. I'm always here to help.

Just dropping by to make sure your concerns are addressed, @lessenberry-anim.

Did the information answer your query about creating a Custom Field drop-down list? If you need more clarification on this process, just let me know. I'll be sure to get back to you.

You're welcome to post again or leave a reply below if you have other concerns with QuickBooks.