In SharePoint, you can use the business connectivity services to get data from various external sources in your lists and libraries.

When migrating lists or libraries with external data, the external data is not preserved.

ShareGate Migrate does not create external content types, so the connection to the external data is not preserved during the migration.

If you create the same external content type at the destination, ShareGate Migrate will preserve the external data in your lists and libraries when you migrate your content.