enforcing function/constant names length in Oracle 18 to be 30 characters in Oracle 18 is there a way to enforce the max length of function names (and constant-names) to be 30 chars only (as it is in Oracle 11 and priors)?
In general it appears that the answer is &quot;no&quot;. Allowable object name length is a function of the COMPATIBLE initialization parameter. See here:

https://docs.oracle.com/en/database/oracle/oracle-database/12.2/sqlrf/Database-Object-Names-and-Qualifiers.html#GUID-05F1B577-C08C-4DB9-925A-8799C76ADFF4

This parameter is usually intended to ensure your ability to downgrade an Oracle version to a previous release following an unsuccessful upgrade. Once set to a higher value, it cannot be lowered again, as it will have an impact on the data dictionary and other Oracle internal features. See here:

https://docs.oracle.com/en/database/oracle/oracle-database/12.2/refrn/COMPATIBLE.html#GUID-6C57EE11-BD06-4BB8-A0F7-D6CDDD086FA9
https://docs.oracle.com/en/database/oracle/oracle-database/12.2/upgrd/tasks-complete-only-manually-upgrading-oracle-database.html#GUID-C2DE66A9-61F0-41AE-A028-FEAC57ECC0BC