I understand that App Registration represents an app that might have UI for users to login. I understand that a Service Principal is for applications like scheduled batch processing applications.
But from the technical perspective, in Azure Portal App Registration list, I can see both of them in the list and look the same.
Is there anything that an SP can do that an App Registration cannot or vice versa?
The App registration is the template used to create the SP. The SP is a security principal (like a User) which can be authenticated and authorized. Follow juunas link, specially Relationship between application objects and service principals.
The App Registrations view shows Azure AD Applications, which are identified by its Application ID, while Enterprise Applications view displays Service Principals. You can navigate from the Application to its associated Service Principal using the link labeled with Managed application in local directory in the Application Overview.
Application and Service Principal are associated by the Application ID. Often they have the same name, but they differ in its Object ID.
Please check the mentioned documentation for the purpose of Applications and Service Principals.
