I tested successfully with modified command line, here share for you:
<qemu:commandline>
<qemu:arg value="-cpu"/>
<qemu:arg value="host,level=30,migratable=on,hv-time=on,hv-relaxed=on,hv-vapic=on,hv-spinlocks=0x1fff,hv-vpindex=on,hv-runtime=on,hv-synic=on,hv-stimer=on,hv-stimer-direct=on,hv-reset=on,hv-vendor-id=whatever,hv-frequencies=on,hv-reenlightenment=on,hv-tlbflush=on,hv-ipi=on,hv-evmcs=on"/>
</qemu:commandline>
put it in VM setting, QEMU command line, update then hyper-v can be started.
Sourcing from: https://gitlab.com/qemu-project/qemu/-/issues/1031