Version 19.17.0.0.0

 1,模拟在备库执行删除undo datafile

alter database recover managed standby database cancel;

alter session set container=appdb;
alter database datafile 11 offline drop;

  select status,FILE#,name from v$datafile where file#=11;

STATUS	     FILE# NAME
------- ---------- --------------------------------------------------
RECOVER 	11 +ARCH/SPDB19C/ED068853EA9868D3E0530B39A8C0E59F/DAT
		   AFILE/undotbs1.623.1156154065

启动日志应用：主库切换几次归档日志切换。

alter database recover managed standby database using current logfile disconnect;

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2,尝试online

对文件执行 oneline 报错：
alter database recover managed standby database cancel;
alter session set container=appdb;
alter database datafile 11 online;

SQL> 
SQL> alter database recover managed standby database cancel;
alter session set container=appdb;
alter database datafile 11 online;alter database recover managed standby database cancel
*
ERROR at line 1:
ORA-16136: Managed Standby Recovery not active


SQL> 
Session altered.

SQL> 
alter database datafile 11 online
*
ERROR at line 1:
ORA-01113: file 11 needs media recovery
ORA-01110: data file 11:
'+ARCH/SPDB19C/ED068853EA9868D3E0530B39A8C0E59F/DATAFILE/undotbs1.623.1156154065
'
SQL> recover datafile 11;
ORA-00283: recovery session canceled due to errors
ORA-01610: recovery using the BACKUP CONTROLFILE option must be done

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3,解决方法

--重启数据库！

shu immediate
startup mount
alter session set container=appdb;
alter database datafile 11 online;