The users appearing in the user field list are determined by the collaborators listed in the miniExtensions Dummy table within your base. To set this up, you can go to the Setup section of the Collaborator field settings.
Click this button only once. If the field is already present in the dummy table, you will observe the following:
Navigate to the Airtable base to locate the dummy table. At times, the table may appear labeled solely as "miniExtensions."
Include all the collaborators you wish to appear in the list within a single record; there's no need to create individual records for each collaborator.
Note
The reason why you need to go through this process is that the Users field is not fully supported by Airtable API. We have to rely on this workaround to resolve that issue.
FAQs
Do I need to do this for each of the collaborator fields in my form?
A: No. All the user fields in the same base share the same list in the dummy table.
Even if I already added a collaborator in the field, it is not showing up in the dropdown of the form. What should I do?
A: If it is not showing up in the list, please follow this article: How to force update changes in Airtable base structure in miniExtensions?