I have provided you with a script how to convert the ObjectGUID of AD User to ImmutableID, but I have forgot to explain you the relation between them.
In Hybrid environment with AD Connect using to sync On-Premise user to Azure AD, with AD Connect set with the default setting:
- AD Connect will calculate the source Anchor based on ObjectGUID
- AD Connect will also sync the User principal Name using the UserPrincipalName Attribute of the user
Please find the step AD Connect will use to Convert ObjectGUID to ImmutableID:
- AD Connect will retreive the User ObjectGUID Attribute through AD Connector
- AD Connect will then convert the ObjectGUID to CloudSourceAnchor(in the Metaverse)
- AD Connect will then export CloudSourceAnchor(Metaverse) to SourceAnchor(AAD Connector)
- The AAD Connector will export SourceAnchor to Azure AD
- The SourceAnchor will be saved as ImmutableID Attribute of Azure AD Object.
I hope this information will help to better understand how your AD Connect is working.