How to set up alert policies in the Compliance Center

If you want to be notified about unusual events happening in SharePoint (i.e., a large number of documents deleted or an unusually large number of files shared externally), you can set up some alert policies in the Microsoft 365 Compliance Center.

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As you migrate your content and intellectual property to OneDrive and SharePoint, it is only natural that, at some point, you might want to take tighter control of your data (documents in this context). For example, you might want to designate certain content to be confidential and have it accessed by only certain employees.

https://sharepointmaven.com/an-overview-of-compliance-features-in-sharepoint-and-office-365/