Sorry for above post - not sure why my post lost all it's formatting of the code.
Anyway - I have solved the issue of the error message :
Property 'sort' does not exist on type 'AggregationState | EntityState | CollectionState'. Property 'sort' does not exist on type 'AggregationState'.
If I don't assign a type to the variable that points to the object that is of type , then this error appears, even though the collection being retrieved from Kinvey is a multi-entity collection, however if I declare it explicitly, then the error dissappears. In either situation the sort order is applied!
eg This returns the error: const categoryInitialState = categoryServiceOptions.initialState;
However, assigning the type explicitly prevents the error message
So, hope this helps someone else at some stage!