The new Search Ads 360 doesn't automatically retrieve social performance and engagement metrics directly from the engine. Instead, you use a PMD or the social engine itself to send metrics to a secure FTP endpoint.
Learn how to create a Google sFTP endpoint in the new Search Ads 360 to import social metrics.
In the new Search Ads 360, one sFTP endpoint can support multiple purposes. Ensure you drop your file to a specific subfolder (not the root folder) to ensure the system recognizes the connection's purpose.