For physical standbys, there is no DBA_* view that I know which tracks the history of switchover and failover. For Logical standby there is DBA_LOGSTDBY_HISTORY.
Ways to find the information are the Dataguard Broker log – when Broker is in use -, or using the database alert log and the following grep command:
$ grep -EB1 '^ALTER DATABASE (SWITCHOVER|FAILOVER) TO' alert_*.log
2023-03-06T14:12:38.905705+01:00
ALTER DATABASE SWITCHOVER TO 'mydb2'
--
2023-03-06T14:37:43.209653+01:00
ALTER DATABASE FAILOVER TO MYDB1
--
2023-03-06T14:38:03.352141+01:00
ALTER DATABASE SWITCHOVER TO PRIMARY (MYDB1)
--
2023-03-11T16:00:22.224218+01:00
ALTER DATABASE SWITCHOVER TO 'mydb2'