I have never tried this, but looking at it now, yes, it is true that you can only map to IFC Properties with the "Single" Property Type, but not when the Property Type is any of the other four types (Enumerated, Bounded, Table, List).
However, after you created the IFC Property, you can go to the File > Interoperability > IFC > IFC Project Manager Dialog, select all the IfcBuildingElement Proxies, and define the Enumerated Values by clicking the ellipsis button (...) in the Value column for the IFC Property.
In the Dialog, you can click the New button to add and define as many enumerated values as you want, then use the checkmarks to the left of their value to select which value the given element uses.
In the below example, I defined 4 values, and used the "CCC" value for the selected element (multiple selections are possible).
I suppose that if you set the proper values for all elements, they will be correctly exported as Enumerated values in the generated IFC file.
One suggestion: GRAPHISOFT recommends that you do not start the name of custom IFC Property groups with "Pset_" because that is the naming used by default IFC Properties. You should use some other naming convention so that you can very easily distinguish between default and custom IFC Properties.
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