To address your issue I have updated some users in my trial tenant account and I am able to get that in UserManagement category in AuditLog Graph API.
As you can see I am getting "Id" for that particular Log. Use this Id in Get Audit Log Graph API. Please refer below screenshot.
Hope this helps.
If the answer is helpful, please click "Accept Answer" and kindly upvote. If you have extra questions about this answer, please click "Comment".