Universal Containers (UC) would like to count the number of open cases associated with each Account and update the Account with this value every Friday evening. UC has several hundred open cases at…

Process Builder is being deprecated in favor of Flow, and while it could be scheduled, a dedicated scheduled flow or a record-triggered flow is the recommended automation solution.

A record-triggered flow on the Case object can be configured to run whenever a Case is created, updated (e.g., its status changes to open or closed), or deleted. This allows the flow to dynamically update a custom number field on the related Account with the current count of open cases in near real-time, providing an up-to-date value for reporting purposes on any given schedule, including every Friday evening.

A scheduled flow could run every Friday evening, iterating through Accounts and querying Cases, but a record-triggered flow offers a more efficient, real-time approach by updating the count only when relevant Case records change, which may be preferred for managing 'several hundred open cases' incrementally.

Roll-Up Summary fields can only be created on master-detail relationships, but Account and Case have a lookup relationship, preventing the direct use of this field type.