KVM + Windows requires x86(-64) hardware. POWER9 and windows means QEMU, which is emulation and slow.
They did experiment with that in fact:
https://www.crowdsupply.com/raptor-computing-systems/talos-s...
https://www.crowdsupply.com/raptor-computing-systems/talos-s...
This means you'll have at least KVM so you can run nearly anything on top of that including Windows VMs with PCI-passthrough for gaming,etc.
The cost is non-trivial but I've been working up my nerve to pull the trigger and go this route.