The AAD Users virtual table in Dataverse has limitations when building apps for the Power Platform. When using a lookup control to display information from the AAD Users table, filtering by lookup column does not return any data. A workaround is to replicate the AAD Users table and get it synched, add additional fields to the related table, or replicate parts of the functionality of the AAD Users table. The author chose to add a Json string to the related table which would contain the AAD User Id, Display Name, UPN/Email and Employee Number. This allowed them to search for a value in the AAD User Json column and count the number of records which they needed as part of the application.
Login now to access my digest by 365.Training