CONFIG_MARCH_G5 is not available for thedefaultarchitecture x86.
Result is shown for architecture s390
default or selected kernelversion does not have config value CONFIG_MARCH_G5.
Result is shown for kernelversion 6.5.1

System/390 model G5 and G6

configname: CONFIG_MARCH_G5

Processor type
└─>System/390 model G5 and G6
In linux kernel since version 2.6.12  
Select this to build a 31 bit kernel that works
on all ESA/390 and z/Architecture machines.

depends
NOT CONFIG_64BIT