Hi @YusukeYamashita-6797 ,
Based on my research and test, I confirm to you that actions taken by users (admins, delegates, and owners) in mailboxes are logged, and activity can be searched using the audit log search tool in the Microsoft 365 compliance center. However, this feature is not currently supported for resource mailboxes. By design, audit log entries can't be generated for room mailboxes, a type of resource mailbox. The same goes for discovery mailboxes.