Yes it really does what its name suggests.

• thunk is the name of the middleware that allows action creators to return functions instead of plain objects. These functions are called with helpful things like dispatch and getState as arguments, so you can orchestrate how other actions are dispatched, wait for asynchronous things, etc..
• Actions creators that return a function instead of an object are also called thunks when the thunk middleware is used in a project
• createAsyncThunk does not replace thunk, it is a more concise way of writing a thunk. They typically follow the same pattern so createAsyncThunk automates that away. createAsyncThunk in fact requires the thunk middleware to be used, which is taken care of by the store setup from redux-toolkit (where createAsyncThunk comes from).