It is very easy to set up free-and-open-source OpenCL computing support if you have an AMD GPU and Debian 11:
apt install ocl-icd-libopencl1 mesa-opencl-icd
clinfo (from the package
clinfo) to display information about your platform.
You can now use
/dev/dri and the files in
/etc/OpenCL to run OpenCL applications.
(Many thanks to the author of this blog post.)