During the upgrade, Oracle set the parameter _pdb_name_case_sensitive to TRUE by default, as explained in Doc ID 2642230.1.
If you then proceeded to convert your old EBS database to a pluggable database with a lower case name, this has the effect that a "flashback pluggable database" operation will fail when using sqlplus:
oracle@oraserver01:[pdb1]# echo $ORACLE_SID
cdb
oracle@oraserver01:[pdb1]# sqlplus / as sysdba
SQL*Plus: Release 19.0.0.0.0 - Production on Tue Aug 6 10:23:55 2024
Version 19.23.0.0.0
SYS@_container_name SQL> show pdbs
CON_ID CON_NAME OPEN MODE RESTRICTED
---------- ------------------------------ ---------- ----------
2 PDB$SEED READ ONLY NO
4 pdb1 MOUNTED
SYS@_container_name SQL> flashback pluggable database "pdb1" to restore point SD76759_1;
flashback pluggable database "pdb1" to restore point SD76759_1
*
ERROR at line 1:
ORA-65011: Pluggable database PDB1 does not exist.
Workaround: Use RMAN instead
oracle@oraserver01:[pdb1]# rman target / Recovery Manager: Release 19.0.0.0.0 - Production on Tue Aug 6 10:26:51 2024 Version 19.23.0.0.0 Copyright (c) 1982, 2019, Oracle and/or its affiliates. All rights reserved. connected to target database: CDB (DBID=2245029826) RMAN> flashback pluggable database "pdb1" to restore point SD76759_1; Starting flashback at 06-AUG-24 starting media recovery archived log for thread 1 with sequence 21576 is already on disk as file /oradisk3/recoveryarea/CDB/archivelog/2024_07_11/o1_mf_1_21576__nw9trq2c_.arc media recovery complete, elapsed time: 00:00:01 Finished flashback at 06-AUG-24