You cannot live-migrate Libvirt VMs between different QEMU versions over SSH (sadly, since that feature is awesome). You can, however, easily perform an offline migration.

I was migrating from Alma 10 to Fedora 43; your QEMU machine types may vary.

First, stop the VM on the source server.

Dump the configuration for the domain:

root@machine0:~# virsh dumpxml file-pub-0.lab.wporter.org > file-pub-0-cfg.xml

Copy the VHD over (typically to /var/lib/libvirt/images), and copy the config over somewhere easily accessible (it’s just going to be used to define the VM in the new spot). scp is nice and easy to use for this (and means your traffic is going over the wire encrypted).

root@machine0:~# scp /var/lib/libvirt/images/file-pub-0.lab.wporter.org.qcow2 machine1:/var/lib/libvirt/images/
file-pub-0.lab.wporter.org.qcow2                                                 100%   64GB  77.8MB/s   14:02

Once you’ve got your files on the destination machine, edit the configured machinetype in the configuration XML file from the unsupported version of QEMU, e.g., pc-q35-rhel10.0.0, to a supported version, e.g., pc-q35-9.2. Example: sed -i 's/pc-q35-rhel10.0.0/pc-q35-9.2/g'.

Once references to unsupported things or nonexistent network interfaces are removed, load the domain on your target system, start it, and off you go:

root@machine1:~# virsh define file-pub-0-cfg.xml