This tip came to me from a question someone posed internally that we had to find an answer for by hunting someone down .
This property isn’t exposed in Server Managers’ UI, so you can set it by calling this powershell command:
Set-RDVirtualDesktopCollectionConfiguration –CollectionName <farm> –CustomRdpProperty “redirectcomports:i:1”
Now the Remote Desktop Client will redirect its COM1 port to the Server. Why is this needed? Think Serially connected devices such as say, Smart Card readers, for instance.
Hope this helps!