Your best option is the Management activities API: https://learn.microsoft.com/en-us/office/office-365-management-api/office-365-management-activity-api-reference
If for some reason you need a PowerShell-based solution, use the Exchange Online module and the Search-UnifiedAuditLog cmdlet search instead of the Graph one: https://learn.microsoft.com/en-us/powershell/module/exchange/search-unifiedauditlog?view=exchange-ps