While doing upgrade database from 12c to 19c
Upgrade Oracle Application Express (APEX) manually before the database upgrade.
The database contains APEX version 5.0.4.00.12. Upgrade APEX to at least version 18.2.0.00.12.
Starting with Oracle Database Release 18, APEX is not upgraded automatically as part of the database upgrade. Refer to My Oracle Support Note 1088970.1 for information about APEX installation and upgrades.
Download APEX 18.2
Install & Upgrade’
move the OLD apex to different location or renam apex to apex_old
Extract the apex and copy to oracle home path.
@apexins.sql SYSAUX SYSAUX TEMP /i/