at the step when it says it doesn't detect any free disk space/volume (i.e. virtio drivers are missing inside the Windows ISO), you can then eject the Windows ISO from ACS (detach ISO), then attach via ACS the previously uploaded VirtIO drives ISO ( https://docs.fedoraproject.org/en-US/quick-docs/creating-windows-virtual-machines-using-virtio-drivers/index.html#virtio-win-direct-downloads), then inside Windows installation "look for drivers" and load the same from the ISO, confirm once or so, and then again detach the VirtIO ISO via ACS and attach the Windows ISO again - there will be one-time warning maybe in Windows setup, but just ask that and continue... This does work - test by me long time ago. If you want to integrate VirtIO drivers inside Windows ISO, that is a different story.
Cheers, Andrija
