The ArcGIS Data Store relational data store has been a required component of a base ArcGIS Enterprise deployment since 10.6. You cannot upgrade directly from ArcGIS Enterprise releases that do not have an ArcGIS Data Store relational data store. Therefore, if you need information about replacing a managed database with a relational data store, see the documentation for the intermediate version to which you will upgrade prior to upgrading to ArcGIS Enterprise 11.3.