This way of creating a Multi-Select dropdown is the fastest and easiest way.
Referencing a System Table (User; Department; Group & Roles)
Steps:
Drag & Drop the control to the form
Change the Server Id: The server Id should always be set the same way, first, it’s the Entity Name followed by the Attribute. The entity name does not exist yet, after saving, it will create the table in the database and it will also be displayed in the Entity form.
Save the form and answer yes to the following questions: