The rxjs operations exported here transform a RxDocument into its underlying Javascript object. data() does this for a single item; datas() does this for an array of items. This "makes useState happy", such that you can re-render a View Component when one or more items it is observing (and transforming to a View) change state.
RxDB queries (and streams of results for queries) return RxDocuments, which are class instances having a plethora of methods on them. These do not play well with React's useState hook, which will not re-render changed data when it is (I am guessing) not in a serializable format? It may be that useState uses referential equality to compare state1 and state2, that the RxDocument, though changed, may be at the same address in memory, so useState sees no change and does't re-rerender. I don't know.
rxdb's recommended method for converting a RxDocument to a serializable format is the method toJSON. However, in practice, this method seems to mutate the RxDocument. I'm not sure why, but when using rxDoc.toJSON() (see below), I was seeing recursive/infinite-loop -type behavior on the Observable. So... use rxDox._data.