In official tutorial saying about changing namespace by cliking on namespace item and set context
But I can't see in my version 2020.3
A namespace is a part of a Kubernetes context, other ones are cluster and user credentials. So essentially a Kubernetes context is a shortcut which gives you a quick access to a namespace in your cluster. For the screenshot you posted, default
namespace has a context created for it (usual scenario), but other namespaces do not have a context.
If you want to create a context for another namespace, please use kubectl config set-context
command in a terminal. Cloud Code doesn't support this operation via UI or Kubernetes Explorer since it's normally rarely used. Contexts are normally created automatically when you start a cluster like minikube or GKE.