CONFIG_ARCH_S390X is not available for the default architecture x86.
Result is shown for architecture s390
default or selected kernelversion does not have config value CONFIG_ARCH_S390X.
Result is shown for kernelversion 5.10.12

64 bit kernel

modulename: entry64.ko
configname: CONFIG_ARCH_S390X

Linux Kernel Configuration
└─> Base setup
└─> 64 bit kernel

Select this option if you have a 64 bit IBM zSeries machine
and want to use the 64 bit addressing mode.

source code: