Jean-Pierre Paradis's Blog: Exchange Online enforces EWSAllowedAppIDs on October 10

Starting October 10, Microsoft will require Exchange Online apps to appear in `EWSAllowedAppIDs` to keep using EWS, following the earlier warning that the allow list would be required. For qualifying Worldwide tenants, Microsoft plans to add IDs on October 8 and 9 based on the previous 60 days of activity—but apps used less often may need to be added manually.

Source : Exchange Online enforces EWSAllowedAppIDs on October 10 – 4sysops