External table datapump column encryption not working

Standalone, 19.17, Oracle Linux

This create-table ...

create table ext_eventlog

(

  EVENTLOG_TYPE,

  EVENTLOG_DATETIME,

  EVENTLOG_SOURCE,

  EVENTLOG_CATEGORY,

  EVENTLOG_EVENT,

  EVENTLOG_USER,

  EVENTLOG_TEXT encrypt using 'AES256' identified by "wutwut",

  EVENTLOG_ID,

  EVENTLOG_APP,

  EVENTLOG_SERVER

)

  organization external(

     type oracle_datapump

     default directory archiver_dir

     location('eventlog.dmp')

  )

as

select *

from asset.eventlog

where rownum <= 10

... runs without error and, does NOT produce a file with encrypted values in the indicated column. Additionally, a second external-table created without the column-encrypt clause reads the file without issue. Sooo, not encrypted.

The tables has no TDE-encrypted columns. The table exists in a TDE-encrypted tablespace.