Explanation
A third-party app can provide a solution for managing volunteer events, such as Volunteerforce or HandsOn Connect, which are available on the AppExchange. Event Monitoring is a feature that tracks user activity and performance, not volunteer events. Process Builder is a tool that automates business processes, not event management. References:
https://trailhead.salesforce.com/en/content/learn/modules/volunteer-management-basics
https://help.salesforce.com/s/articleView?id=sf.event_monitoring.htm&type=5
https://help.salesforce.com/s/articleView?id=sf.process_overview.htm&type=5