Controller not detected by steam

[Keplyx]

I tried the app on a linux machine, everything worked as expected (server starts, app connects, and system detects the controller), but I am unable to play on steam with it.

Here is the server's console output after starting the server with start.sh in dist/linux and connecting a controller:

Server addresses:
wlp2s0 http://192.168.43.202:31415/

Starting server...
Sat, 15 Jun 2019 10:29:38 +0200 | INFO   | server     |  | Serving using application   : ./bin/ws_handler 
Sat, 15 Jun 2019 10:29:38 +0200 | INFO   | server     |  | Serving static content from : .
Sat, 15 Jun 2019 10:29:38 +0200 | INFO   | server     |  | Starting WebSocket server   : ws://Bender2:31415/
Sat, 15 Jun 2019 10:29:38 +0200 | INFO   | server     |  | Serving CGI or static files : http://Bender2:31415/
Sat, 15 Jun 2019 10:30:03 +0200 | ACCESS | http       | url:'http://192.168.43.202:31415/' | STATIC
Sat, 15 Jun 2019 10:30:04 +0200 | ACCESS | session    | url:'http://192.168.43.202:31415/' id:'1560587404750222708' remote:'192.168.43.1' command:'./bin/ws_handler' origin:'http://192.168.43.202:31415' | CONNECT

Here is the controller in the system settings (detecting joystick movement and button presses):

Is there a specific option in steam to enable for it to detect the controller?

I am using Kde Neon (based on Ubuntu 18.04).

[Beliriel]

I have the same issue but on Windows. Buttons/Joysticks don't get recognized. And I'm connected to a controller session.

[danvim]

It can be used in conjunction with https://www.x360ce.com/