In sharepoint line for a site I have a few site owners. One owner has stopped inheriting permissions for a library and a folder and gave access to a user. As a tenant admin I want to know who that owner has provided access and breaked the permissions . Is there any powershell script or csom to know it.
You can use the cmdlet
Search-UnifiedAuditLog to search the unified audit log, which requires the Exchange Online PowerShell V2 module to work.
See the sample script via this link: SharePoint Online: How to View Audit Log Reports in Security & Compliance Center?
You can find the available Operations on Site permissions activities here.