If you are using RDS, you generally need both . You need a Windows Server CAL to legally access the server OS, and an RDS CAL to legally use the graphical interface features.
You cannot mix Per User and Per Device in the same environment for the same user. remote desktop services licensing
Unlike older Terminal Services, you don’t license the server’s CPU or OS. You license the client accessing the desktop or app. If you are using RDS, you generally need both
