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

Kernel Userspace Execution Prevention

configname: CONFIG_PPC_KUEP

Linux Kernel Configuration
└─>Processor support
└─>Kernel Userspace Execution Prevention
In linux kernel since version 5.1 (release Date: 2019-05-05)  
Enable support for Kernel Userspace Execution Prevention (KUEP)

If you're unsure, say Y.