you can just use the --opencl-device-types 1 (or short -D 1) command line argument to filter your cpu devices.
Of course the correct OpenCL driver (also make sure which version numbers hashcat suggests) must be installed.
This is also explained in the --help output:
... and no, it's not possible to run hashcat on CPUs/GPUs that do not support OpenCL at all (I'm refering here to your sentence "I want to run CPU-only without OpenCL", you might use hashcat-legacy for that case <- unrecommended because hashcat-legacy will not be updated frequently)
Of course the correct OpenCL driver (also make sure which version numbers hashcat suggests) must be installed.
This is also explained in the --help output:
Quote:-D, --opencl-device-types | Str | OpenCL device-types to use, separate with comma | -D 1
...
# | Device Type
===+=============
1 | CPU
... and no, it's not possible to run hashcat on CPUs/GPUs that do not support OpenCL at all (I'm refering here to your sentence "I want to run CPU-only without OpenCL", you might use hashcat-legacy for that case <- unrecommended because hashcat-legacy will not be updated frequently)