Hi @Vishnu Anand,
I would like to make a sincere apology for the delay, because it took me a while to find other solutions.
Regarding your question, you can try using the Alert Policy in Microsoft Defender.
Here are the specific steps:
1.Navigate to Alert policy and login.
2.New Alert Policy.
3.Name your alert, categorize it, and choose a severity.
4.Choose Shared file externally activity, conditions and when to trigger the alert.
5.Specify who will receive this notification.
6.Open the policy and submit.
7.This way when a user shares a file for an external user, the recipient receives an email like this:
8.Click View alert details > View activity list >Sharingset. In the list you can see who shared the file, which file was shared and to whom.
9.This is only for sharing files to external users, you can create another policy, but with Share file or folder activity.
If you have any questions, please do not hesitate to contact me.
Moreover, if the issue can be fixed successfully, please click "Accept Answer" so that we can better archive the case and the other community members who are suffering the same issue can benefit from it.
Your kind contribution is much appreciated.