You don’t have to install OpenCL, it comes with your GPU (graphics card) drivers.
You may have to uninstall the ‘Microsoft OpenCL Compatibility Pack’ (or its equivalent on Windows 11), as it seems to be broken.
If your only GPU is the one built into the processor (CPU), it may or may not be strong enough to help with performance.
You can find more info on OpenCL, its usage by darktable, and troubleshooting steps here:
https://darktable-org.github.io/dtdocs/en/special-topics/opencl/
https://darktable-org.github.io/dtdocs/en/special-topics/opencl/problems-solutions/
https://darktable-org.github.io/dtdocs/en/special-topics/opencl/still-doesnt-work/