With the release of Confluence 7.3.1 on feb 5 2020, the support of 19c is added. I tought that with the release of Crowd version 4 on feb 25 2020, the database support for Oracle would also be updated. To bad nothing is happend with this ticket, still gathering interest and no assignee...
Support for Oracle 19c database has been added in Crowd 4.1 which was released today (https://confluence.atlassian.com/crowd/crowd-4-1-release-notes-1004960631.html).