Use host CPU Passthrough: Instead of a generic "kvm64" CPU, pass the "host" CPU model to the VM so Windows 10 can use all modern instruction sets.
qemu-img convert -f vhdx -O qcow2 win10_source.vhdx win10_fixed.qcow2 Windows 10 Qcow2 Download Fixed
Optimized Settings: Many fixed images have telemetry and unnecessary background services disabled to improve performance in virtual environments. Where to Download Windows 10 Qcow2 Images Use host CPU Passthrough: Instead of a generic