ora-49204: recursive dde invocation at phase i - after switchover to standby
Per Oracle Support, this is probably a bug
https://support.oracle.com/knowledge/Oracle%20Database%20Products/2322290_1.html

Function kcidr_file_header_check_common is File Header check which cause of this issue. If you see this in the Stack Trace and Standby opens Read only successfully then you are most likely encountering this bug.