I’ve spoken in the past about the utility of blockchain, to create a table that can not be altered. Oracle 21C is not available in OCI.
The syntax to create a blockchain table is quite simple.
create blockchain table test (x number)
NO DROP UNTIL 30 DAYS IDLE
NO DELETE LOCKED
HASHING USING "SHA2_512" VERSION "v1";
The addition of the blockchain keyword, the options no drop until <>, no delete, locked, and specifying the hashing algorithm and version.