default or selected kernelversion does not have config value CONFIG_CXL_KERNEL_API.
Result is shown for kernelversion 5.4.33

CONFIG_CXL_KERNEL_API (not configurable)

configname: CONFIG_CXL_KERNEL_API

Linux Kernel Configuration
└─>Device Drivers
└─>Misc devices
└─>CXL_KERNEL_API
In linux kernel since version 4.2 (release Date: 2015-08-30)