Currently, there is no way for miniExtensions to know all the Airtable users that can be used in the user field. Our forms can only suggest users that are saved in your existing records.
The workaround is to create a dummy record in Airtable where all of your users are saved in the user field.
💡Note
It may take some for the Airtable users to show up in the drop-down selection since we cache it every 30 minutes.