User Fields can be converted into Multiple Choice/Dropdown Select fields using Patient Displays. To create a multiple choice field, go to Advanced Maintenance > Patient > Displays > (Select a Patient Display)  > Edit (selected display) > Demographic Configuration.
Add the relevant User Field to the Demographic Configuration. On the Edit popup, you can add and modify the choices to be used for that User Field.

Make sure the Display is assigned to the appropriate Document Type(s), and the dropdown menu will show in both InScribe and InQuiry. You may need to log out and back in to the system to see any recent updates to a Patient Display such as this.