No multiple screens on Linux?

I’m trying to use 2 monitors under Linux 20.04. I use an nVidia GPU. I set up monitors as screen 0 and screen 1. They work perfectly fine with the psychtoolbox. However when I try to use psychopy and select screen=1, I receive a warning telling me that screen 1 does not exist and the window is always opened on screen 0. Am I doing anything wrong? Is there a way to use 2 monitors under Linux?