Disable the Grant Access Using Hierarchies setting on the Case object. This maps the scenario to the Salesforce-native capability that owns the requirement.

The Core Concept Explained: Experience Cloud design is driven by persona, authentication, scale, and sharing. The wrong template or license can create unnecessary cost, weak security, or excessive customization.

Step-by-Step Technical Analysis: Begin with the external persona, authentication requirement, and transaction volume. Select the Experience Cloud license or template that matches that access pattern, then configure sharing sets, external OWD, site visibility, and page access. Finish by testing the experience as anonymous, authenticated, and internal users. Disable Grant Access Using Hierarchies on the Case object where supported for the Employee Experience security design.

Why the Incorrect Options Are Wrong: A points to a disablement approach that either is not supported for the tested feature or would remove a capability the scenario depends on. B does not meet the implementation-quality bar for security, scale, auditability, or maintainability in this scenario. D does not meet the implementation-quality bar for security, scale, auditability, or maintainability in this scenario.