Autonomous Data Guard is a feature of Autonomous Database on Shared Infrastructure that provides data protection and disaster recovery for your database by creating and maintaining a standby database that continuously gets updated with the changes from the primary database4. With Autonomous Data Guard enabled, you can perform a switchover or a failover operation to switch roles between the primary and standby databases. A switchover is a planned role reversal that does not affect availability5. A failover is an unplanned role reversal that occurs when the primary database becomes unavailable due to a failure or disaster6. You cannot perform a reinstate operation, which is used to re-synchronize a disabled standby database with the primary database after a failover7. You also cannot change the protection mode, which determines how redo data is transmitted from the primary database to the standby database4. You can only view the apply lag, which is the difference between the redo applied on the standby database and the redo generated on the primary database5. Reference:
Use Standby Databases with Autonomous Data Guard for Disaster Recovery - Oracle Help Center.
Switch Roles in an Autonomous Data Guard Configuration - Oracle Help Center.
Fail Over to the Standby in an Autonomous Data Guard Configuration - Oracle Help Center.
Reinstate the Disabled Standby in an Autonomous Data Guard Configuration - Oracle Help Center.

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