If there were a virtual kubelet per unit of granularity (datacenter, in their case?) then you would be able to use affinity rules just fine.
The press release states that your k8s API is actually running on a single machine with k3s and a virtual-kubelet. So, I’m not sure if it’s one “cluster” per region, or one “cluster” with multiple virtual-kubelets for regions.
Either way, your FKS cluster control-plane would sit in a single region.