CONFIG_KVM_SW_PROTECTED_VM is not available for thedefaultarchitecture x86.
Result is shown for architecture 64BIT

Enable support for KVM software-protected VMs

configname: CONFIG_KVM_SW_PROTECTED_VM

Linux Kernel Configuration
└─>Virtualization
└─>Enable support for KVM software-protected VMs
In linux kernel since version 4.19.310 (release Date: 2024-03-15)  
Enable support for KVM software-protected VMs. Currently, software-
protected VMs are purely a development and testing vehicle for
KVM_CREATE_GUEST_MEMFD. Attempting to run a "real" VM workload as a
software-protected VM will fail miserably.

If unsure, say "N".