By default, two concurrent sessions are available for Windows RDP. If you want more, you must order RDS CALs from Microsoft. Please refer to https://www.microsoft.com/en-us/store/d/Windows-Server-2016-Remote-Desktop-Services/DG7GMGF0DS1H/0006?SilentAuth=1&wa=wsignin1.0 or https://www.microsoft.com/en-us/p/windows-server-remote-desktop-services-cal/dg7gmgf0dvsv?activetab=pivot%3aoverviewtab.