Cockpit can manage virtual machines running on the host. These can be accessed from menu via Virtual Machines
Primary datasource is QEMU / Libvirt, access to Libvirtd is wrapped either by the virsh tool or libvirt D-Bus API bindings, depending if the latter is installed on the system. If libvirt-dbus package is not available in your distribution's software repositories you can follow the instructions here to install from sources.
In order to run cockpit-machines plugin inside a virtual machine
or run the tests for this component, you'll need nested KVM virtualization enabled
(refer test/verify/nested-kvm or
How to enable nested virtualization in KVM to get more information).
In order to manipulate as unprivileged user VMs on system connection through cockpit-machines plugin using libvirt D-Bus provider you need to follow the instructions specified here.