"From the perspective of a guest operating system, a virtual network connection is the same as a physical network connection. Host machines view virtual network switches as network interfaces. When the libvirtd service is first installed and started, it creates virbr0, the default network interface for VMs.
#Virtualization #KVM #Linux #Debian #libvirt #virbr0
https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/8/html/configuring_and_managing_virtualization/configuring-virtual-machine-network-connections_configuring-and-managing-virtualization

Notes for future me:

whenever #libvirt is installed, the default network (virbr0) is not autostarted.

To make it appear on "ip show link", enter on virsh and execute
"net-autostart --network default" and then "net-start --nertwork default".

With the commands above #virbr0 shall appear and ready to be used by #qemu.