Create RKE2 cluster

I am trying to create a RKE2 rancher cluster using this guide: Terraform Registry

I am in an air gapped environment and need to also set the default system registry, but the section indicates that auth_config_secret_name should be set to a K8s secret. How can this secret exist prior to cluster creation?

Documentation could be a little better.
The secret that is used for auth_config_secret_name should be a secret that is on the K8s cluster for the Rancher server itself, and under the fleet-default namespace