Managed Apple IDs are used in accessing Apple services using Apple Business Manager. These user accounts are created through integration with a third party identity provider (IDP) such as Azure Active Directory. By default, these Apple Business Manager Managed Apple IDs are created using the User Principal Name in the IDP but can be changed by an admin.
For Shared iPad users to receive the correct apps and profiles, the Managed Apple ID of the user logging into the device must match an enrollment user within Workspace ONE UEM. By default, Workspace ONE UEM assumes the Email Address value of the enrollment user is the Managed Apple ID. If your users require a different Managed Apple ID format, you can edit this in the Settings.
To know more about Shared iPad with Managed Apple IDs, see Apple Documentation here.