You need to perform the steps listed below to configure BIOVIA Direct after upgrade from Oracle 12 to Oracle 19C. If not, you will see ORA errors listed below.

ORA-06520: PL/SQL: Error loading external library
ORA-06512: at "C\\\$DIRECT2021.MDLAUXOP", line 2364
ORA-06512: at "C\\\$DIRECT2021.MDLAUXOP", line 2361

Steps to be Performed:
1. Edit listener.ora and correct the LD_LIBRARY_PATH to point to bin19 for example, u01/app/BIOVIA/DIRECT2021SP1/bin19
2. Restart the database listener and DIRECT2021 listener.
3. Edit mdllibdef.sql in the folder u01/app/BIOVIA/DIRECT2021SP1/sql to correct the path to point to bin19.
4. Connect as system and run mdllibdef.sql
5. Connect as system and run mdltestlistener.sql from u01/app/BIOVIA/DIRECT2021SP1/sql folder
6. Connect as C\\\$DIRECT2021 schema and run the command below to verify that BIOVIA Direct is working without any ORA errors.
Select mdlaux.version from dual;

7. Connect as each schema used by BIOVIA Direct, for example, SYMYXDB and run the following commands and verify there are no ORA errors.
execute mdlaux.unsetup;
execute c\\\$direct2021.mdlauxop.setup;
select mdlaux.version from dual;