CONFIG_MAXPHYSMEM_128GB is not available for thedefaultarchitecture x86.
Result is shown for architecture 64BIT or riscv
default or selected kernelversion does not have config value CONFIG_MAXPHYSMEM_128GB.
Result is shown for kernelversion 6.9.9

128GiB

configname: CONFIG_MAXPHYSMEM_128GB

Maximum Physical Memory
└─>128GiB
In linux kernel since version 3.10 (release Date: 2013-06-30)