Microsoft 365 preserves your orphaned user values in Person or group fields (i.e., Created by and Modified by) when you migrate your content in Insane mode.
Insane mode uses the Microsoft 365 migration API, allowing the migration tool to set orphaned users in these fields.
Limitations
Some Insane mode limitations can cause a list or library to migrate in Normal mode instead. When this occurs, orphaned users are no longer preserved.
Deleted SharePoint groups are not supported.