It looks like setting Feedback off suppresses error reporting in all recent versions of SQLcl. In SQLPlus, error reporting is not suppressed by setting feedback off.
Here is an example using the latest SQLcl version:
SQL>
SQL> show version
Oracle SQLDeveloper Command-Line (SQLcl) version: 19.1.0.0
SQL> set feedback on
SQL>
SQL> select * from qwefewf;
Error starting at line : 1 in command -
select * from qwefewf
Error at Command Line : 1 Column : 15
Error report -
SQL Error: ORA-00942: table or view does not exist
00942. 00000 - "table or view does not exist"
*Cause:
*Action:
SQL>
SQL> set feedback off
SQL>
SQL> select * from qwefewf;
SQL>
SQL>
SQL> set headings off
SQL> select * from dual where 1=2;
SQL>
This must be a bug, not a feature - when feedback is set off, there is no difference between output from a successful SQL statement and output from a failed statement. This is dangerous!