The legacy Hive metastore is maintained for backward compatibility.  When you start using Unity Catalog compatible compute i.e. when the workspace has an assigned Unity Catalog metastore, and the cluster is in access mode 'Shared' or 'Single User', or in SQL warehouses then you to reference a fully qualified 3 level name. Catalog.Schema.table.

Run the following SQL queries to check if Unity Catalog is enabled and to list the catalogs and schemas.