CONFIG_ARM64_SME is not available for thedefaultarchitecture x86.
Result is shown for architecture arm64

ARM Scalable Matrix Extension support

configname: CONFIG_ARM64_SME

Linux Kernel Configuration
└─>Kernel Features
└─>ARM Scalable Matrix Extension support
In linux kernel since version 5.2 (release Date: 2019-07-07)  
The Scalable Matrix Extension (SME) is an extension to the AArch64
execution state which utilises a substantial subset of the SVE
instruction set, together with the addition of new architectural
register state capable of holding two dimensional matrix tiles to
enable various matrix operations.