You have a Microsoft 365 E5 subscription that uses Microsoft Purview.

Comprehensive Detailed Explanation with References

Custom Data Access Governance (DAG) data assessment scans in Microsoft Purview can be run on selected SharePoint Online or OneDrive locations to check for oversharing and exposure. Each custom assessment scan supports up to 200,000 items per location. This cap is documented in Microsoft’s guidance for custom data access governance assessments.