You're right, your constraints have to be immediate for DML error logging to catch them.

I'm not aware of a way for you to capture the invalid rows on commit.

What you could do is:

- Before committing, setting the fk(s) to immediate (set constraint .. immediate)
- If this throws an exception, run a query to find the invalid rows

create table t1 (x primary key) as
  select rownum x from dual connect by level <= 10;
 
create table t2 (
  t1x int constraint fk references
    t1 (x) deferrable initially deferred
);

insert into t2 values (0);

set constraint fk immediate;

SQL Error: ORA-02291: integrity constraint (CHRIS.FK) violated - parent key not found

select * from t2
where  not exists (
  select * from t1
  where  x = t1x
);

       T1X
----------
         0

You'll need to update your code to do this and capture the invalid rows and log them. You can't find this information out "after the fact".