There have been som issues with the addon not installing it correctly on blender. I`m going to share my experience that others can get som info on the matter.
i`m running a ryzen 1700 and rx580 setup dual booting linux and windows, and since Linux is my main OS here are some tips and tricks. Note that this is for Kubuntu 20.04 LTS and it may apply to other Ubuntu based distros.
RPR needs OpenCL to run and to install, and since AMD just released an updated gpu driver for 20.04 its less of a workaround now. What RPR also needs is a working and teste version of Vulkan, that isn't mentioned to much and people forget (myself included). Since the introduction of Full spectrum rendering the Addon reqiures it and causes error if it does not detect the corect one. (im not a developer i'm stating my observations)
Since AMD drivers are open source they come preinstalled in the linux Kernel but proper suport for OpenCL and Vulkan do not. Using the famous Oibaf PPA for the bleeding edge drivers do indeed install Vulkan libraries, however they are not suported and cause issues during the activation of the addon.
So what i recomend Linux Users with AMD hardware is to:
1) uninstall any amd-gpu and amd-gpu-pro drivers (fully) by running the script from /usr/bin/ the script is called amdgpu-pro-uninstall.
2) remove any other open source drivers (in my case Oibaf's PPA, while great they are only usefull for gaming performance), followed by a clean-up from commands like sudo apt autoremove, sudo apt clean, sudo apt autoclean.
3) download the latest amd drivers for ubuntu, unpack it and open a terminal inside the unpacked drivers runing the following command:
sudo ./amdgpu-pro-install -y --opencl=pal,legacy --headless
(this will install opencl and will work inly for Blender Cycles nothing more)
sudo ./amdgpu-pro-install -y --opencl=pal,legacy
(this will install Opencl suport and updated tested vulkan, use this if you want to run Luxcore and RPR with no issues)
4) reboot the OS (and considering that you are not running a custom kernel or other modifications to the OS graphics drivers) and everything should be fine.
5) navigate to the home folder and enable hidden files visibility, where in the /.config/blender/2.xx/addons/ make sure you do not have any remaining folders from previous RPR attempts, also make sure you dont have any remains of the addon in Blender as well by searching for it and clicking the remove button in the blender addon manager.
6) download latest RPR addon, restart blender and everything should work fine bouth in installing it and enableing it.
Note that the Linux version does not suport some features yet and dont support all hardware's, AI denoising stops the viewport from rendering also using the low,mid,high preset in the settings are buggy and in my case work really slow compared to windows on the same hardware, this is because this presets uses Vulkan entirely not OpenCl or CPU.
Good luck and i hope this helps someone!