Oracle 19c is supported with EPM 11.1.2.4 but there is an unpublished bug which can be mitigated with a setting on the database.
The following entries need to be added to the Oracle Database SQLNET.ORA file and the client SQLNET.ORA
SQLNET.ALLOWED_LOGON_VERSION_CLIENT=8
SQLNET.ALLOWED_LOGON_VERSION_SERVER=8
Restart the DB.
Ref Doc ID 2320228.1