Explanation
An alert policy consists of a set of rules and conditions that define the user or admin activity that generates an alert, a list of users who trigger the alert if they perform the activity, and a threshold that defines how many times the activity has to occur before an alert is triggered.
In this question, we would use the "Malware detected in file" activity in the alert settings then configure the threshold (5 detections) and the time window (10 minutes).
The ability to configure alert policies based on a threshold or based on unusual activity requires Advanced Threat Protection (ATP).
Reference:
https://docs.microsoft.com/en-us/microsoft-365/compliance/alert-policies