EWS enforcement starts October 1. $true with no AppID list blocks everything. $null isn't blocked on day one, but gets flipped to $false later.
Known apps and AppIDs to allow-list or migrate:
lazyadmin.nl/office-365/k...
lazyadmin.nl
Known EWS Apps that need Allow-Listing or a Migration - with AppIDs
Microsoft starts enforcing the EWS AppID allow-list on October 1, 2026. Here are the known apps and AppIDs that still use EWS, and which ones you can migrate.