To create a new VMnet, select the Host object and navigate to its Networks tab.
Choose your vswitch, and select Add VMnet within it.

Name your new VMnet, and choose which VLAN ID to use for it.
0 will set traffic to untagged
After pressing confirm, you should see your new VMnet appear on the vswitch. You will note however that there are no VMs connected to the VMnet yet.

To connect a VM to a VMnet, you can either modify an existing network connection to “move” it to the new network, or you can add a new network connection to the VM. VMs can be connected to multiple VMnets, but whether you choose to do so depends on your specific use case.
Network entry, and press the Add button
virtio connection type should only be selected after installing the VM's guest tools (more info)Your VM will now be connected to the new network.

Network entry, and find the network connection you want to change

Your VM will now be disconnected from the original network, and instead connected to the new network

TBA
see HCUI