Per OTN support Doc ID 2500405.1, we are supposedly able to "downgrade" the 19C EM interface from Jet to Flash since the Jet version in 19c is not yet fully functional.
To that end, the related DocID provides a command that fails when copied-n-pasted directly from the OTN DocID:
SQL> @?/rdbms/admin/execemx emx
It fails with:
ERROR at line 1:
ORA-06550: line 1, column 7:
PLS-00201: identifier 'PRVT_EMX' must be declared
ORA-06550: line 1, column 7:
PL/SQL: Statement ignored
See attached ullustration
Can someone please explain how it is that an Oracle supplied SQL file supplied in this installation created folder (\rdbms\admin) fails to execute?
And, more importantly, can someone please provide a viable, working command that we can execute in order to revert to utilizing the EM Flash interface instead of the not-ready-for-prime 
time Jet-based Em interface, pleeeeease?
(https://support.oracle.com/epmos/faces/DocumentDisplay?_afrLoop=456076248775177&parent=EXTERNAL_SEARCH&sourceId=REFERENC… )