Checking GPU usage:
Ubuntu: Click on “Ubuntu software” and search for ‘psensor‘ if the usage is less then 100% you may consider running multiple BOINC clients.
OpenCL:
Ubuntu: Make sure the GPU drivers are installed: ‘sudo ubuntu-drivers autoinstall’
The OpenCL interface might not be installed, do so with ‘sudo apt install ocl-icd-libopencl1’