eDiscovery case (Premium) and on-premise file share content

What you’re running into is actually a limitation of how Microsoft Purview treats graph connector data today. Graph connectors can index content from on-premises file shares and make it available for Microsoft Search. Still, they are not yet supported as a discoverable data source in Purview eDiscovery (Premium). That’s why when you create a case, you don’t see an option to add your connector as a source — the eDiscovery workflow only supports Microsoft 365 native workloads like Exchange Online, SharePoint Online, OneDrive, Teams, Viva Engage, and some third-party archiving connectors that have been integrated explicitly for compliance.

In your setup, the graph connector is working correctly, indexing the file share and making the content searchable through Microsoft 365 search experiences. The missing piece is that Purview eDiscovery Premium does not extend to this connector content. Currently, the supported route for on-premises file shares is either to migrate or copy the data into a supported cloud repository (for example, SharePoint Online or OneDrive for Business), thereby bringing it under Purview eDiscovery, or to utilize third-party eDiscovery/archiving tools for hybrid coverage.

you haven’t misconfigured anything, the feature doesn’t exist yet. Suppose your compliance team needs those on-prem file shares included in Purview eDiscovery Premium. In that case, the practical solution is to plan a migration of that data into Microsoft 365 or use a supported ingestion path that Purview recognizes as an eDiscovery source.