Windows Server 2016 and 2019 comes with a new HTML5 based RDP Web Client, allowing users to access computers and applications in the browser.
The HTML5 based RDP Web Client is currently not supporting mapping local printers from the client computer, therefore no printers will be mapped by Print2RDP or Microsoft EasyPrint during the RDP session in the browser.
Currently there is no workaround for this limitation.
When connected through the HTML5 based RDP Web Client, a Remote Desktop Virtual Printer will be mapped by Microsoft. Printing to the Remote Desktop Virtual Printer will download the printed document in the client browser as PDF.