The Teams Versions Overview report shows all Team Clients versions that were used in calls in the tenant in the last 7 days. This overview shows clients regardless of whether that are on monitored or unmonitored devices. Per version it shows the number of devices using it and the users involved.
It categorizes them by Operating system and version and indicates how many versions of the Windows client are older than 90 days. Under Microsoft-controlled rollout schedules versions exceeding 90 days are classified as outdated.