CONFIG_RISCV_ALTERNATIVE is not available for thedefaultarchitecture x86.
Result is shown for architecture riscv

CONFIG_RISCV_ALTERNATIVE (not configurable)

modulename: alternative.ko

configname: CONFIG_RISCV_ALTERNATIVE

Linux Kernel Configuration
└─>Platform type
└─>RISCV_ALTERNATIVE
In linux kernel since version 4.14.326 (release Date: 2023-09-23)  
This Kconfig allows the kernel to automatically patch the
erratum or cpufeature required by the execution platform at run
time. The code patching overhead is minimal, as it's only done
once at boot and once on each module load.

source code: