You can download a ready-to-use Windows 10 QCOW2 image for QEMU/KVM from these sources (always check for the latest version):
Get the VHDX file
Visit Windows 10 Enterprise Evaluation
Select “Download – VHDX” (64-bit). windows 10qcow2 download new
Convert VHDX to QCOW2
qemu-img convert -O qcow2 windows10-evualation.vhdx windows10.qcow2
Resize (optional)
qemu-img resize windows10.qcow2 50G
If you are managing multiple QCOW2 images, "new" means "latest updates." Use HashiCorp Packer to automate building a fresh Windows 10 QCOW2 daily or weekly. You can download a ready-to-use Windows 10 QCOW2
Microsoft provides Windows 10 Enterprise evaluation VHDX images. You can download and convert to QCOW2: Get the VHDX file Visit Windows 10 Enterprise
qemu-img:
qemu-img convert -O qcow2 Windows10.vhdx Windows10.qcow2
This is the best way to get a new (latest updates), clean, and safe QCOW2 file.
win10.qcow2):
qemu-img create -f qcow2 win10.qcow2 50G