default or selected kernelversion does not have config value CONFIG_KVM_DEVICE_ASSIGNMENT.
Result is shown for kernelversion 6.5.1

KVM legacy PCI device assignment support

configname: CONFIG_KVM_DEVICE_ASSIGNMENT

Linux Kernel Configuration
└─>Virtualization
└─>KVM legacy PCI device assignment support
In linux kernel since version 3.1 (release Date: 2011-10-24)  
Provide support for legacy PCI device assignment through KVM. The
kernel now also supports a full featured userspace device driver
framework through VFIO, which supersedes much of this support.

If unsure, say Y.