I’m sorry I can’t help you much. I have personally never used a AMD GPU on Linux and so haven’t faced the problem of OpenCL not being detected. However this thread might contain some useful information: Guide | Install AMD OpenCL on: Pop!OS & some Ubuntu Derivates | Linux, amdgpu, amdgpu-pro, rocm, rocr
As for the HIP implementation, it is disabled by default and is thus not accessible to the end user. However you can compile Blender with HIP if you want to test it, I’m just not sure if it works with the publicly available GPU drivers and HIP compiler. You should wait until official build instructions are released by AMD/Blender developers.