As the screenshot says, you need to decide which cluster the node should be able to join, in order to create it.
It's a common mistake even with physical clusters. But this name can't be decided for you because a new node (not this one, but Element nodes in general) may be deployed to an environment where multiple clusters are found on the same management network)
Go to https://node-management-ip:442/config/#/cluster
There enter your desired cluster name, and then Save. After that you can create cluster at https://node-management-ip/createcluster
(By the way Element Demo VM is not really a simulator, although it's commonly referred to because ONTAP has a simulator VM... It's a Demo VM that can create a single-node cluster with almost all Element features as production clusters)