WORKAROUND 1
In the link above, it is suggested by Oracle to revert the Oracle behavior back to before, however,that might force you to lose the benefit of the intended change by Oracle.
WORKAROUND 2
We offer another workaround within SQL Navigator to get it working without impacting other sessions of the Oracle database:
1. Save the following SQL into a file:
alter session set events='10946 level 65536';
2. In SQL Navigator, go to View | Preferences... | General | Session | Auto Run Script | Auto run script at connect.
Select the sql file just saved. Press Ok to save Preferences.
3. Close all sessions in SQL Navigator and make a connection again to the 18c database.
4. Recompile the package that has arguments of nested data types.
5. Now you should be able to Execute/Run functions in the package without error.
