Kerberos constrained delegation is intended to be used by services and not regular users. Active Directory distinguish service users from regular users whether the user has an SPN registered or not. Regular users have no SPN registered while service users could have one.
The Delegation tab in the user's properties within Active Directory Users and Computers is only available if an SPN is configured. In order to use Kerberos constrained delegation, any SPN must be configured for the system user.