Yes, you would just attach it to the network switch and have it join the cluster.
The control plane will "discover" the additional capacity and redistribute workloads if necessary.
With k3s, a new node can join the cluster with a single command (assuming you have the API token).
Something like:
$ curl -sfL https://get.k3s.io | K3S_URL=https://$YOUR_SERVER_NODE_IP:6443 K3S_TOKEN=$YOUR_CLUSTER_TOKEN sh -