I have been using Microsoft Remote Desktop client for macOS to connect to remote Windows 10 computers and have the RDP client forward my smart card over to the remote machine. I don't use the smart card for login to the remote machine, but I use it once forwarded with the browser to login to a PIV enable website.
This has all been working fine until recently it stopped working. The version I currently have is ithe 10.6.8 version that is published in the Mac App Store and I also tried the latest beta release.
If I go to a Windows 10 computer and forward the smart card to the same remote PC it works just fine (using the same card and reader). So, it seems like something has broken in a recent version of the client.