Since update to Fedora 38 using vagrant --debug up displays
INFO machine: Initializing machine: default
INFO machine: - Provider: VagrantPlugins::ProviderLibvirt::Provider
INFO machine: - Box: #<Vagrant::Box:0x00007f45425ac7b8>
INFO machine: - Data dir: /home/user/vagrant/.vagrant/machines/default/libvirt
INFO driver: Connecting to Libvirt (qemu:///session) ...
It is usually socket activated, that is virtnetworkd.socket is enabled and active, and when virtnetworkd.serviceis needed it will be started automatically.