So I just inherited a system with an RX 480 as the gpu. Right off the bat I’ve been having issues. I installed Ubuntu 20.04 but I had to use the boot flag nomodeset in order for the USB key to work. The PC is connected via HDMI to a 4k screen. During the initial installation process and without that boot flag the PC immediately goes to a black screen after grub. I tried to fix this by updating the kernel to the 5.8 version but this just causes the system to not boot at all. The nomodeset flag no longer works on that kernel version and removing that causes the computer to not work at all. I tried using the amdgpu.dc=0 but that also fails to work. Any assistance with getting the PC to work with the appropriate drivers and audio will be greatly appreciated.
Just to report with an update that I reinstalled Ubuntu 20.04 and haven’t changed from the 5.4 kernel but my issue with a black screen still persist. I have even downloaded and installed the amd gpu drivers but there is still a black screen after grub.
Try booting the pc without the monitor plugged in then connect it after a minute or so. It will force the display to the native resolution. Once you are in the GUI you can set the display settings to hidpi and it should work from there.
It’s an annoying issue with Linux that should not be a thing in 2020
Usually RX 400 and RX 500 series are rock solid gpus in Linux. The AMDGPU driver comes with the kernel, they are basically plug and play.
Have you tried with another monitor or TV?
Check if your GPU supports dual bios, if it does, try the other one. I had a similar issue with my XFX RX 580. The “high performance” bios makes my monitor “sleep”. With the “normal” bios, the GPU works flawlessly.