Varela states it is not possible to have a representation of the world as there is not a ‘thing’ in the real world. But I don’t use models in that way. A model is a representation of the world but there is no need for that to be an accurate representation of the world. It just needs to be useful.

The arguments against mental representations goes beyond what you mention here. The arguments don't pertain to whether there is an external reality, they pertain to how the mind works. Enactivism posits that nervous system is informationally closed and a dynamic system.