Per Oracle 19c document - "Archived historic data that has aged beyond the specified retention period is automatically purged". However, that's not happening when I tested it.
I created an archive with retention of 1 day and did quite a lot DML. A few days or even weeks later, all the archived records are still in the SYS_FBA_HIST_x table. And when I run "select * from dba_flashback_archive", the LAST_PURGE_TIME has the same value as in the CREATE_TIME column.
Not sure what I missed here. I tried 12c and 19c, using accounts with and without DBA privilege, and with cases of within the quota and out of the quota.