From what i know latest driver won't work with claymore (and other miners). You need to revert to the 18.04 ones. Here how it worked for me on Ubuntu 20.04 with RX580 8GB (same setup as you)
make sure you have hwe installed
sudo apt-get install --install-recommends linux-generic-hwe-20.04
make a backup of /etc/os-release and edit it.
sudo cp /etc/os-release ~
sudo nano /etc/os-release
Check for the VERSION_ID and change it from "20.04" to "18.04"
Make sure you remove previoulsy installed driver
amdgpu-pro-uninstall
The driver version 19.50 worked for me, try lower version if it fails.
Download, Extract and install it:
wget https://drivers.amd.com/drivers/linux/19.50/amdgpu-pro-19.50-967956-ubuntu-18.04.tar.xz --referer https://support.amd.com/
tar -Jxvf amdgpu-pro-19.50-967956-ubuntu-18.04.tar.xz
cd amdgpu-pro-19.50-967956-ubuntu-18.04
./amdgpu-pro-install -y --opencl=pal,legacy,rocm --headless --no-dkms
Replace the original /etc/os-release file
mv ~/os-release /etc/os-release
Not sure about this but i did it, add yourself to the video and render group
sudo usermod -a -G video $LOGNAME
sudo usermod -a -G render $LOGNAME
Finally reboot
sudo reboot now
Even clinfo will tell your device are OpenCL capable and will detect them but for some reason the miner won't. Hope this works.
Best Answer
The release download page is here
Download the *.deb (Debian) file, e.g. Ethereum-Wallet-linux64-0-9-0.deb
Then do: