I tried to run az provider register --namespace Microsoft.ContainerService with more than 2 hours. However, it still shows WindowsPreview in NotRegistered status.
It mentioned only It takes a few minutes for the registration to complete in this link but it has been taking more than 2 hours.
The right command should be this:
az feature register --name WindowsPreview --namespace Microsoft.ContainerServiceAnd the command you run is to refresh the registration of the Microsoft.ContainerService resource provider.
Even though the answer is provided by Charles, i would like to attach the list of commands that would help others,
az feature register --name "WindowsPreview" --namespace "Microsoft.ContainerService"and list of commands