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

xtheadvector extension support

configname: CONFIG_RISCV_ISA_XTHEADVECTOR

Linux Kernel Configuration
└─>Vendor extensions
└─>T-Head
└─>xtheadvector extension support
In linux kernel since version 6.6.78 (release Date: 2025-02-17)  
Say N here if you want to disable all xtheadvector related procedures
in the kernel. This will disable vector for any T-Head board that
contains xtheadvector rather than the standard vector.

If you don't know what to do here, say Y.