Standby database is now supported in Autonomous Database. When you enable Autonomous Data Guard on ADB support only 19c and above version. (Except Always-Free Tier). If your primary database goes down, Autonomous Data Guard converts the standby database to the primary database with minimal interruption. After failover completes, Autonomous Data Guard automatically creates a new standby database.
Customer is able to perform a switchover operation, where the primary database becomes the standby database, and the standby database becomes the primary database.
The system creates a standby database that stays "connected" to the primary database and automatically refreshes its data from the primary database.
Autonomous Database does not provide access to the standby database.