I just had a look at the installation instructions you posted, the download links there point to the release from a year ago and there are newer ones: Releases · GPUOpen-LibrariesAndSDKs/RadeonProRenderBlenderAddon · GitHub
I tried getting them to work by adding with pkgs; [ libGL stdenv.cc.cc.lib vulkan-loader rocm-opencl-icd rocm-opencl-runtime "$HOME/.config/blender/2.93/scripts/addons/rprblender" ] to my LD_LIBRARY_PATH when starting blender.
That seems to enable the plugin to load, but blender crashes with
mesa: CommandLine Error: Option 'help-list' registered more than once!
LLVM ERROR: inconsistency in registered CommandLine options
(I also marked all the *.so files as executable, not sure if that makes a difference.)
I guess multiple LLVM versions get loaded and clash, but I don’t understand why it loads mesa, even if I force amdvlk with VK_ICD_FILENAMES=/run/opengl-driver/share/vulkan/icd.d/amd_icd64.json.