Docker desktop kubernetes add node
As far as I'm aware, you cannot add a node to Docker for Desktop with Kubernetes enabled.
Docker for Desktop is a single-node Kubernetes or Docker Swarm cluster, you might try using kubernetes-the-hard-way as this explains how to setup a cluster and add nodes manually without the use of kubeadm.
But I don't think this might work as there will be a lot of issues with setting up the network to work correctly.
You can also use the instructions on how to install kubeadm with kubelet and kubectl on Linux machine and adding a node using kubeadm join.