Brand new install of Windows 2016 Server Evaluation without any updates installed, specific build 14393.rs1_release.161220-1747 (also 14393.447) Attempting to remote desktop to the server from a Windows 10 client resulted in an error:
An authentication error has occurred.
The function requested is not supported
This could be due to CredSSP encryption oracle remediation. For more information, see https://go.microsoft.com/fwlink/?linkid=866660
Note: For Windows 7 clients, the last line above in red color will be omitted from the error message.
This happened for both Datacenter and Standard installs of the same build. The fix is to simply install all available updates from Windows Update, rebooting in between as necessary. After all updates have been installed, try the remote connection again.