What can High Volume Community users access if they can access a record's parent?

High Volume Community users can access records that have a Controlled by Parent sharing setting if they can access the parent record. This sharing model means that the sharing settings for a child record are directly determined by the sharing settings of its parent record. Therefore, when High Volume Community users have access to a parent record, they inherently gain access to the child records associated with it, as the sharing is managed in a way that ties the access rights of the child to the parent.

The Controlled by Parent setting facilitates a streamlined access mechanism, allowing users to interact with related records in a logical and structured manner, ensuring that the users have visibility into relevant information without needing separate permissions for every single record.

Other options, while they might indicate various access points, do not align with the specifics of the Controlled by Parent sharing setting. For instance, sharing groups or records without ownership would not inherently grant access the same way as the Controlled by Parent setting does. Accessing all records within the community is also broader than the situation defined by the question, as it does not specifically relate to the parent-child relationship in the context of sharing settings.