SharePoint Online generates a lot of events in the Office 365 audit log. You can interrogate the log with PowerShell to create per-user reports of their activities. The Search-UnifiedAuditLog cmdlet finds all the necessary data; after that it’s just a matter of filtering and refining the data and then creating the reports.
https://office365itpros.com/2020/05/13/generate-per-user-audit-reports-sharepoint-online-activity/
