Oracle Database 21c is now available for download for Linux platforms.
Download here!
This workshop offers several hands-on labs
Oracle Database 21c contains more than 200 new innovations, including immutable blockchain tables, In-Database JavaScript, native JSON data type, AutoML for In-Database Machine Learning (ML), persistent memory store and sharding.
More details on new features in Oracle 21c can be found in Learning Database New Features
For details about database releases and their support timeframes, refer to Doc ID 742060.1 on My Oracle Support.