default or selected kernelversion does not have config value CONFIG_ARCH_DISCARD_MEMBLOCK.
Result is shown for kernelversion 6.9.9

CONFIG_ARCH_DISCARD_MEMBLOCK (not configurable)

configname: CONFIG_ARCH_DISCARD_MEMBLOCK

Linux Kernel Configuration
└─>Memory Management options
└─>ARCH_DISCARD_MEMBLOCK
In linux kernel since version 3.1 (release Date: 2011-10-24)