It appears that, at minimum, the macOS RDP client does not default the smart card redirection RDP property redirectsmartcards to 1 as defined at Supported RDP properties with Remote Desktop Services | Microsoft Learn. This property must be explicitly set to 1 by the Remote Desktop Service (RDS) in the RDP file it provides to the client in order for smart card redirection to be enabled for the session on macOS. When the property is not specified at all, smart card redirection is enabled on Windows clients, but not on macOS clients. Manually editing the .RDP file provided by the server to set redirectsmartcards:i:1 works. However, it seems that the macOS client should use the same RDP property defaults as the Windows client as defined in the article referenced above. I am running macOS client version 10.8.1.
