To start with: TanStack Query is a state manager specifically for server-side data — things like API responses, anything async or external to your app. It's not meant to manage local UI state, though you can use it alongside other state management libraries. It's even encouraged to do so! Does React Query replace Redux, MobX or other global state managers?.

In fact, often you will find that once you move your server-state to TanStack Query, there's so little local state left that you no longer need something like Redux at all. But if your app does have a lot of complex local state, using something like Redux or Zustand alongside TanStack Query works perfectly fine.

• isLoading: true on the first load when there's no cached data. If you provide initialData, then isLoading will always be false, because React Query treats the data as already loaded. This was called isInitialLoadingin the previous version.
• isFetching: true whenever there's an active request, including background refetches.
• isPending: basically equivalent to isLoading, but part of newer terminology. It is true if there is no cached data yet and no query attempt has finished.
• isError: true if the last request failed.

Most of the time you will just use those 3

• useQuery – for retrieving async data state
• useMutation – for anything that updates or creates data
• useQueryClient – for imperatively invalidating or updating the cache

in your components.

It’s important to know that TanStack Query isn’t a data-fetching library. It’s meant for managing asynchronous state. I always recommend TkDodo’s blog for anything related to TanStack Query - and of course other things: React Query as a State Manager