When creating an Infrastructure, use the Enable GKE toggle switch to enable GKE. In the Cluster Mode list box, select GKE Autopilot. Complete the remaining fields (GKE Version, GKE Endpoint Visibility, and Cluster IP CIDR). Click Create.
This takes about 20 minutes. Infrastructure status should move to Completed. Once the Infrastructure status shows Complete, navigate to Administrators -> Plans to verify that a Plan has been created with the same name (nonprod).