I have a new Dell Precision 7730 laptop and I have installed Xubuntu on it, everything works except the fact that I can't connect my second external monitor to it with an HDMI cable (which works just fine on Windows).

The computer has a hybrid graphics card system. Running lspci -nn | grep -E 'VGA|Display' gives:

00:02.0 VGA compatible controller [0300]: Intel Corporation Device [8086:3e94] 01:00.0 VGA compatible controller [0300]: Advanced Micro Devices, Inc. [AMD/ATI] Baffin [Radeon Pro WX 4130/4150] [1002:67e8]

And according to xrandr:

HDMI-1 disconnected (normal left inverted right x axis y axis)

I have installed the amdgpu-pro drivers (following the tutorial on ATI's website) and I still can't fix it. The only weird thing is that, when I shut the computer down, the second monitor briefly turns on and shows the Xubuntu splash image before shutting down.

Does anyone know how to fix this problem?