When you download from the server, you almost always receive a file. Understanding the difference is key for local development: Tableau Server Data Sources
GET /api/api-version/sites/site-id/datasources/datasource-id/content
Follow these steps to retrieve a published data source from your Tableau Server environment:
On the left navigation pane, select Explore , then click the Data sources tab to see all published connections.
Downloading a data source from Tableau Server allows you to work with metadata, calculated fields, and connection settings locally in Tableau Desktop. This process is distinct from simply exporting raw data to a CSV or Excel file; it retrieves the (Tableau Data Source) or .tdsx (Packaged Data Source) file that defines how Tableau interacts with your data. Prerequisites and Permissions