Explanation
A scheduled flow is a type of flow that runs at scheduled times on batches of records that meet certain criteria.
It can be used to count the number of open cases associated with each account and update the account with this value every Friday evening by using an assignment element to loop through the accounts and cases and assign the count value to a field on the account record. Using a record trigger flow, a scheduled process builder, or a roll-up summary field are not suitable options for this requirement because they would not run at scheduled times or on batches of records; they would run every time a record is created or updated, which may not reflect the accurate count of open cases at the end of each week. References:
https://help.salesforce.com/s/articleView?id=sf.flow_concepts_scheduled.htm&type=5