CONFIG_CPU_MIPSR5 is not available for thedefaultarchitecture x86.
Result is shown for architecture mips

CONFIG_CPU_MIPSR5 (not configurable)

configname: CONFIG_CPU_MIPSR5

Linux Kernel Configuration
└─>CPU_MIPSR5
In linux kernel since version 5.1 (release Date: 2019-05-05)