Hi,
Thank you for your feedback.
In StarUML, Subsystem view element do not support attributes or operation compartment even if you can add attributes and operations to the Subsystem model element. So you cannot drop attributes and operations on the Subsystem view in diagram.
Subsystem is an abstraction of a sub-system of a larger system, and we don't think it's a good idea to represent its detailed attributes in a diagram. Keep it simple.
Thanks,