In a 20.04 VM, we can see that linux-image-kvm doesn't have the module enabled while linux-image-virtual and linux-image-generic have it:
# grep CONFIG_VHOST_NET /boot/config-5.4.0-1*
/boot/config-5.4.0-1070-kvm:# CONFIG_VHOST_NET is not set
/boot/config-5.4.0-121-generic:CONFIG_VHOST_NET=m
In a 20.04 VM, we can see that linux-image-kvm doesn't have the module enabled while linux-image-virtual and linux-image-generic have it:
# grep CONFIG_VHOST_NET /boot/config- 5.4.0-1* 5.4.0-1070- kvm:# CONFIG_VHOST_NET is not set 5.4.0-121- generic: CONFIG_ VHOST_NET= m
/boot/config-
/boot/config-