The correct option is project_ws.get_default_datastore().

This Workspace method returns the workspace default Datastore object which you can use to read and write files and to connect datasets and compute against the workspace storage.

project_ws.get_dataset() is incorrect because the Workspace API does not expose a method by that name and dataset retrieval is handled through the Dataset APIs rather than a workspace method for datastores.

project_ws.default() is incorrect because there is no such method on the Workspace class and it will not return the default datastore.

project_ws.find() is incorrect because this is not the documented way to retrieve the workspace default datastore and it does not return the Datastore object that get_default_datastore does.

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