Notify admin when user is copying/downloading/deleting data

[null null]

How can we achieve below task in OneDrive for business.

If any user is copying / downloading / deleting data more than --- MB or  ___ no. of files from One Drive, then system should send an email alert notification to Administrator. At the same time, activity should NOT be restricted for user.

[#2]

At this moment there isn't any feature available to control what you mentioned. Raising a UserVoice might be the way to go

[#3]

Do you mean without being and Admin of the users' ODFB? The only way you have to do some "monitoring" on behalf of end users is by means of the Audit Log Search

[#4]

The only tool that allows you to configure something like this is the activity policies functionality in MCAS: https://docs.microsoft.com/en-us/cloud-app-security/user-activity-policies