Oracle 18c

By using db<>fiddle, you agree to license everything you submit by Creative Commons CC0.

ALTER SESSION SET NLS_DATE_FORMAT = 'YYYY-MM-DD HH24:MI:SS';
ALTER SESSION SET NLS_TIMESTAMP_FORMAT = 'YYYY-MM-DD HH24:MI:SS.FF9';
SELECT TO_TIMESTAMP( '19-01-21 09:15:00.000000 PM', 'DD-MM-RR HH12:MI:SS.FF6 AM' )
         AS timestamp_value
FROM   DUAL;

TIMESTAMP_VALUE

2021-01-19 21:15:00.000000000

SELECT CAST(
         TO_TIMESTAMP( '19-01-21 09:15:00.000000 PM', 'DD-MM-RR HH12:MI:SS.FF6 AM' )
         AS DATE
       ) AS date_value
FROM   DUAL;

DATE_VALUE

2021-01-19 21:15:00

SELECT TO_DATE( '19-01-21 09:15:00.000000 PM', 'DD-MM-RR HH12:MI:SS".000000" AM' )
         AS date_value
FROM   DUAL;

DATE_VALUE

2021-01-19 21:15:00