Orphaned users' metadata is preserved when copying to Microsoft 365. This capability relies on a Microsoft Microsoft 365 API update and on a feature automatically enabled on the destination Microsoft 365 tenant. In Insane Mode, Created by, Modified by and custom Person or Group field values are preserved.
Any content copied through the normal SharePoint API will not feature the preserved users values and metadata. The Insane Mode limitations also apply to this feature.
Deleted SharePoint groups are not supported.