Per the new Horizon Update for Attribute feature you can now edit searchability within the C360 layout:

However for low volume object that are editable we are still unable to searches within the user object or person object. Can you please help us figure out why search-ability is not possible for low-volume objects.
Use case: Account Team low volume object to be able to do manual assignments for CSMs, Success executives, professional services, Technical account managers, ETC.
This is our current view for add new records within low volume in the new horizon.

We would like to search for an email address within user object for this field.