The reason why this error is raised is because the T4 card doesn’t have a display.
In our case, we have an onboard Intel graphics, to which X11 is attached. T4 is used only for an inference.
Now that I found the answer, a graphics card has to have a display out (and perhaps which is connected with an actual display) to show a window by a deepstream running in a docker container, will mark this as solved.