CONFIG_KVM_ARM_MAX_VCPUS is not available for thedefaultarchitecture x86.
Result is shown for architecture arm
default or selected kernelversion does not have config value CONFIG_KVM_ARM_MAX_VCPUS.
Result is shown for kernelversion 6.5.1

Number maximum supported virtual CPUs per VM

configname: CONFIG_KVM_ARM_MAX_VCPUS

Linux Kernel Configuration
└─>Virtualization
└─>Number maximum supported virtual CPUs per VM
In linux kernel since version 3.1 (release Date: 2011-10-24)  
Static number of max supported virtual CPUs per VM.

If you choose a high number, the vcpu structures will be quite
large, so only choose a reasonable number that you expect to
actually use.