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I moved the NVME drive from my old computer (Ryzen 2600x with Nvidia) to new one (Ryzen 4750G with Radeon). In the new setup, only the monitor connected to the DisplayPort monitor is working with Ubuntu. Any monitor I connect to the HDMI port, even using different cables, never works and appears that Ubuntu never detects it. When I am accessing the BIOS, the HDMI monitor works fine.

I believe the cause of the issue is that I moved the NVME drive from a Ryzen 2600x w/Nvidia card to Ryzen 4750G w/Radeon.

Based on some googling, I have tried xrandr to setup the HDMI but I get these issues:

Output from xrandr:

xrandr: Failed to get size of gamma for output default
Screen 0: minimum 2560 x 1440, current 2560 x 1440, maximum 2560 x 1440
default connected primary 2560x1440+0+0 0mm x 0mm
   2560x1440     93.00* 

When I tried xrandr --addmode HDMI 2560x1440_60.00:

xrandr: Failed to get size of gamma for output default
xrandr: cannot find output "HDMI"

I also tried variations of the above command with --addmode HDMI0 and --addmode HDMI1 but got similar output.

I would prefer not to reinstall Ubuntu if possible.

Any suggestions?

EDIT:

Output from dpkg -l | grep nvidia after I remove NVIDIA drivers using sudo apt purge libnvidia* xserver-xorg-video-nvidia-390 and sudo apt-get remove --purge '^nvidia-.*':

ii  libnvidia-compute-450:i386                 450.80.02-0ubuntu0.20.04.2            i386         NVIDIA libcompute package
ii  libnvidia-decode-440:i386                  450.80.02-0ubuntu0.20.04.2            i386         Transitional package for libnvidia-decode-450
ii  libnvidia-decode-450:i386                  450.80.02-0ubuntu0.20.04.2            i386         NVIDIA Video Decoding runtime libraries
ii  libnvidia-encode-450:i386                  450.80.02-0ubuntu0.20.04.2            i386         NVENC Video Encoding runtime library
ii  libnvidia-fbc1-450:i386                    450.80.02-0ubuntu0.20.04.2            i386         NVIDIA OpenGL-based Framebuffer Capture runtime library
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    Thanks @user68186 - I ran sudo apt-get remove --purge '^nvidia-.*' and rebooted. It removed some nvidia stuff but the problem remains. – Wonko the Sane Dec 4 '20 at 17:23
  • Thanks @user68186 - I have updated the post to show the output after removing nvidia drivers. I don't think the removal was completely successful. – Wonko the Sane Dec 4 '20 at 17:39
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I got a big hint on how to solve this when I came across this command:

sudo lshw -c display

In the output, I got *-display UNCLAIMED message. After some googling I came across this great and from bertm: Can't get internal and external monitor working simultaneously with 20.04 on laptop with AMD Ryzen 7 4800H and Nvidia RTX 2060

By using the experimental support for Renoir in the Linux kernel that ships with Ubuntu 20.04 I was able to get both monitors working. Here is how I enabled it:

sudo nano /etc/default/grub

Next, add amdgpu.exp_hw_support=1 to GRUB_CMDLINE_LINUX_DEFAULT. Mine looked like this:

GRUB_CMDLINE_LINUX_DEFAULT="quiet splash amdgpu.exp_hw_support=1"

Save changes and then update grub:

`sudo update-grub`

Reboot and it worked for me.

I hope this is useful to others.

Credit to bertm here: Can't get internal and external monitor working simultaneously with 20.04 on laptop with AMD Ryzen 7 4800H and Nvidia RTX 2060

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