CREATE OR REPLACE FUNCTION TEST_SUBSELECT
    (i_firstname in varchar)
RETURN types.cursorType
IS
    o_cursor types.cursorType;
BEGIN
    OPEN o_cursor FOR
    SELECT * FROM party WHERE firstname LIKE '%' || i_firstname || '%';
    
    return o_cursor;
END;
 12  /

Function created.

SQL> select * from TABLE(test_subselect('foo'));
select * from TABLE(test_subselect('foo'))
              *
ERROR at line 1:
ORA-22905: cannot access rows from a non-nested table item