How to backup VM from bhyve and migrate it to KVM?

I am stuck here and can not find information about migrating Windows and Linux/Unix vm's to KVM. Doing it with zfs is inefficient, because it will transfer the whole disk space, which can be more than 200GB. Making a copy of the directories in Linux/Unix machines kind of worked, but I don't think that's the right way. cp -R /etc cp -R /home/user And send those copies to the KVM machine. For the Linux part was basically that. I needed mainly installed services and their configs. If there is a way to copy the entire VM and spin it up on KVM good, I am open. Creating a backup of Windows Server does not work also, because it creates vhdx files and converting them to qcow2 seems to break them, or I just don't do it right. I use the Backup service and add the whole system backup zip to a network share. Basically that's it and I am stuck how it can but used to spin up new Windows VM on KVM. Can someone give me guidance here?