CONFIG_VIRTIO_UML is not available for thedefaultarchitecture x86.
Result is shown for architecture um

UML driver for virtio devices

modulename: virtio_uml.ko

configname: CONFIG_VIRTIO_UML

Linux Kernel Configuration
└─>UML driver for virtio devices
In linux kernel since version 4.14.326 (release Date: 2023-09-23)  
This driver provides support for virtio based paravirtual device
drivers over vhost-user sockets.

source code:
selects
CONFIG_VIRTIO