Source: pyopencl Version: 2021.2.9-1 Followup-For: Bug #1001545 Reading the history further, mesa-opencl-icd was replaced by pocl-opencl-icd | opencl-icd for 2016.1+git20161003-2, commit 3b0d193c, "pocl-opencl-icd is the best default choice when there no other OpenCL ICD installed as it uses CPU and no specialized hardware"
But that was only for the binary package Depends. The source package Build-Depends: pocl-opencl-icd was added much later for 2020.2.2-1, Commit 0000f815 Would we more packaging stability that respects the intention to use pocl-opencl-icd where available if we switch to Build-Depends: mesa-opencl-icd | pocl-opencl-icd | opencl-icd with python3-pyopencl Depends: pocl-opencl-icd | mesa-opencl-icd | opencl-icd i.e. use mesa-opencl-icd to build the package, and prefer pocl-opencl-icd to use it.