Explanation:

Box 1: An Azure Log Analytics workspace
To be able to create an alert we send the Azure AD logs to An Azure Log Analytics workspace.
Note: You can forward your AAD logs and events to either an Azure Storage Account, an Azure Event Hub, Log Analytics, or a combination of all of these.
Box 2: Log
Ensure Resource Type is an analytics source like Log Analytics or Application Insights and signal type as Log.
Reference:
https://4sysops.com/archives/how-to-create-an-azure-ad-admin-login-alert/
https://docs.microsoft.com/en-us/azure/azure-monitor/platform/alerts-log