You can use an eDiscovery case to create and manage eDiscovery holds that can be applied to user mailboxes and other content locations in Microsoft Purview1. You can also use an eDiscovery case to search for and export content from mailboxes and other locations1.
An eDiscovery case is different from a Litigation Hold, which is a hold that is applied to user mailboxes in Exchange Online1. A Litigation Hold isn't identified by a GUID1.
A sensitive info type is a predefined or custom entity that can be used to identify and protect sensitive data in Microsoft Purview2. It is not related to placing a hold on email messages.
A data loss prevention (DLP) policy is a policy that helps prevent the accidental or intentional sharing of sensitive information outside your organization2. It is not related to placing a hold on email messages.
An information barrier segment is a group of users who are allowed or blocked from communicating with each other in Microsoft Teams or SharePoint Online2. It is not related to placing a hold on email messages.