default or selected kernelversion does not have config value CONFIG_DEVKMEM.
Result is shown for kernelversion 6.9.5

/dev/kmem virtual device support

configname: CONFIG_DEVKMEM

Linux Kernel Configuration
└─>Device Drivers
└─>Character devices
└─>/dev/kmem virtual device support
In linux kernel since version 2.6.26 (release Date: 2008-07-13)  
Say Y here if you want to support the /dev/kmem device. The
/dev/kmem device is rarely used, but can be used for certain
kind of kernel debugging operations.
When in doubt, say "N".