default or selected kernelversion does not have config value CONFIG_KMEMCHECK_ENABLED_BY_DEFAULT.
Result is shown for kernelversion 6.5.1

enabled

configname: CONFIG_KMEMCHECK_ENABLED_BY_DEFAULT

kmemcheck: default mode at boot
└─>kmemcheck: trap use of uninitialized memory
└─>enabled
In linux kernel since version 2.6.31 (release Date: 2009-09-09)