For a given policy in Cisco Umbrella, how should a customer block website based on...

To block a website based on a custom list, the customer should add the websites to a blocked type destination list. A destination list is a custom list of domains or URLs that the customer wants to allow or block for their identities. The customer can create destination lists through the Policy Components > Destination Lists page, or within the policy wizard when creating or editing a policy. The custom URL destination block lists feature enables Umbrella to extend a domain level block list to encompass full and partial URLs. In turn, this allows the customer to block certain portions of a website based specifically on the full or partial URL. This feature requires the customer to enable the intelligent proxy and install a root certificate for SSL decryption. References:

Configure Web Policies and Destination Lists - Cisco Umbrella

Control Access to Custom URLs - Umbrella SIG User Guide

Cisco 350-701: How should customer block websites based on custom list

Umbrella Dashboard: New Features—Custom blocked URLs

Understanding Destination lists supported entries and … - Cisco Umbrella