To enable concurrent Remote Desktop (RDP) sessions in Windows 11, you need to make a small change to termsrv.dll file. This file is located in C:\Windows\System32 folder. Before modifying termsrv.dll for the first time, you need to take ownership and assign yourself full permissions. You also need to stop the Remote Desktop service (TermService), if it's running.
DLL files can be modified using any HEX Editor (for example Tiny Hexer). You can do this yourself by replacing the strings shown below, or just download patched versions from this page.
Windows 11 x64 v21H2 - October 2021 Update
The original Windows 11 version (21H2) has termsrv.dll file v10.0.22000.318 To enable concurrent remote desktop connections, make the following changes:
39 81 3C 06 00 00 0F 84 4F 68 01 00
B8 00 01 00 00 89 81 38 06 00 00 90