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
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 intructions specified here.