CONFIG_POWERPC64_CPU is not available for thedefaultarchitecture x86.
Result is shown for architecture powerpc

Generic (POWER5 and PowerPC 970 and above)

configname: CONFIG_POWERPC64_CPU

CPU selection
└─>Generic (POWER5 and PowerPC 970 and above)
In linux kernel since version 4.14.326 (release Date: 2023-09-23)