There is a work around.
AppGate creates a remote desktop file with no extension called "keyless_rdp_ desktop_1" in:
%USERPROFILE%\AppData\Roaming\appgate\11.2.2\rdp\
Add "Use Multimon:i:1" at the end of the file and add the extension ".rdp" to the file "keyless_rdp_desktop_1"
Double click the rdp file and you will get a dual-monitor remote desktop. Make sure AppGate is still connected while doing this.
Each time you disconnect and reconnect AppGate, you will have to reconfigure "Use Multimon:i:1" into the newly created "keyless_rdp_desktop_1" file.
The proper way to do the configuration is to ask the AppGate server keepers to enable the dual-monitor on the server side for you instead of hacking the "keyless_rdp_desktop_1" rdp file.
After it is enabled on the server, you will need to install the AppGate Hosts File Writer (aghostsd.exe) so that AppGate can write dynamic configurations into your host file in C:\Windows\System32\drivers\etc\hosts
Please refer to :
PDF Manual AppGate Security Server - Cyxtera
https://sdpdownloads.cyxtera.com/files/download/AppGate-11.3-LTS/doc/manual.pdf