spark.password {{secrets/scope1/key1}} is spark property and than it will be available in all notebooks via spark.conf.get("spark.password") (we add in Spark config for cluster)

SPARKPASSWORD={{secrets/scope1/key1}} is environment variable (we add it in Environment variables in cluster config)

The problem is that with a standard account you have access to secrets anyway - all of them. In premium, you could make different scopes and set one of them to be accessible only to users who create.start cluster (environment variable) so then people running notebooks will have no access to that secrets.