A Scheduled Automation using a Send Activity is ideal for sending emails to a data extension that is regularly updated. This approach allows for efficient and timely sends without the overhead of journey management, making it suitable for periodic newsletters with dynamic subscriber lists.
Reference:
Salesforce Help: Automation Studio Activities

Explanation
To use Case data from Service Cloud as part of their current email messaging campaign, Northern Trail Outfitters should use Synchronized Data Extensions on the Case Object with a Boolean filter on the Contact Me field. Synchronized Data Extensions are data extensions that allow marketers tosync data from Sales Cloud or Service Cloud objects into Marketing Cloud using filters and schedules. Using Synchronized Data Extensions on the Case Object with a Boolean filter on the Contact Me field will allow Northern Trail Outfitters to import cases that indicate the customer wants someone to contact them after the case is closed.
References:https://help.salesforce.com/s/articleView?id=sf.mc_co_synchronized_data_sources.htm&type=5