For your information, since version 18c (released in July 2018), the Oracle database does support PRIVATE temporary tables which are valid/available solely during the current transaction.

Pragmatic info here: https://oracle-base.com/articles/18c/private-temporary-tables-18c

Official documentation here: https://docs.oracle.com/en/database/oracle/oracle-database/18/admin/managing-tables.html#GUID-6EB347F0-64BA-4B15-8182-41BA7D5A876F