Hey guys. I have the (k)ubuntu 18.04 LTS but just decided to extract the opencl libraries and drivers manually from the pro drivers. Users cannot be expect to do this, but gives a far cleaner install IMO.
The opensource drivers work great for display and eevee. One thing to remember about about the opencl drivers is that they are separate and unrelated to display drivers.
You only need these libraries (re: 18.20 opencl that I’m using) extracted.
libamdocl12cl64.so
libamdocl64.so
libamdocl-orca64.so
libcltrace.so
libOpenCL.so
libOpenCL.so.1
Put in a custom lib directory and add an entry to /etc/ld.so.conf.d run ldconfig. Make sure you have proper *.icd entries in /etc/OpenCL/vendors
test with clinfo (apt install clinfo).
If clinfo sees it blender should also.