Hi,
There is a recent bug in the exercise whereby the resource group name doesn't get set as it should. Below instructions will allow you to complete the exercise.
Please navigate to the Create an Azure virtual machine exercise, Activate a new sandbox, sign in, etc. Once sandbox is activated and black cloud shell window with "Welcome to Azure Cloud Shell" displayed, navigate to Exercise - Configure network access using the "Unit x of 14" dropdown above the exercise.
After page loads and resource group name is updated to learn-, immediately navigate back to Create an Azure virtual machine exercise and complete it.
Inspiration for above workaround came from @pnaroju's #2 suggestion in this post.
Please click Accept Answer and upvote if the above was helpful.
Thanks.
-TP