Hi,
If used on Windows Server, an RDS CAL and Windows Server CAL would be required for each device/user. Below excerpt is from the Product Terms for Windows Server, Access Licenses, RDS CALs:
*Also required for use of Windows Server to host a graphical user interface (using the Windows Server 2022 Remote Desktop Services functionality or other technology).
In essence, if hosting a graphical user interface then an RDS CAL/SL is required. Doesn't matter if you are using some, all, or none of RDS features.
https://www.microsoft.com/licensing/terms/welcome/welcomepage
-TP