SQL> with t(str) as (select '(()(()' from dual),
  2       permute(ord, str, delta)
  3       as (select level ord, str, length(replace(str, ')')) - length(replace(str, '(')) delta
  4             from t
  5           connect by level <= length(replace(str, ')'))),
  6       rec(lvl, ord, str)
  7       as (select 1, ord, regexp_replace(str, '\(', '', 1, ord)
  8             from permute p
  9           union all
 10           select rec.lvl + 1, p.ord, regexp_replace(rec.str, '\(', '', 1, p.ord - rec.lvl)
 11             from rec join permute p on p.ord > rec.ord
 12            where lvl < p.delta),
 13       candidates
 14       as (select distinct str
 15             from rec
 16            where rec.lvl = (select delta from permute where rownum = 1)),
 17       rec_check(iter, str, result)
 18       as (select 1, str, replace(str, '()') result from candidates
 19           union all
 20           select iter + 1, str, replace(result, '()') result
 21             from rec_check
 22            where iter < 2)
 23  select str
 24    from rec_check
 25   where iter = (select delta from permute where rownum = 1)
 26     and result is null;

STR
--------------------------------------------------------------------------------
(())
()()

SQL> with t(str) as (select '((()()((())(()' from dual),
  2       permute(ord, str, delta)
  3       as (select level ord, str, length(replace(str, ')')) - length(replace(str, '(')) delta
  4             from t
  5           connect by level <= length(replace(str, ')'))),
  6       rec(lvl, ord, str)
  7       as (select 1, ord, regexp_replace(str, '\(', '', 1, ord)
  8             from permute p
  9           union all
 10           select rec.lvl + 1, p.ord, regexp_replace(rec.str, '\(', '', 1, p.ord - rec.lvl)
 11             from rec join permute p on p.ord > rec.ord
 12            where lvl < p.delta),
 13       candidates
 14       as (select distinct str
 15             from rec
 16            where rec.lvl = (select delta from permute where rownum = 1)),
 17       rec_check(iter, str, result)
 18       as (select 1, str, replace(str, '()') result from candidates
 19           union all
 20           select iter + 1, str, replace(result, '()') result
 21             from rec_check
 22            where iter < (select delta from permute where rownum = 1))
 23  select str
 24    from rec_check
 25   where iter = (select delta from permute where rownum = 1)
 26     and result is null;

STR
--------------------------------------------------------------------------------
(()()())()
(()()(()))
(())(())()
((())(()))
((())())()
()()((()))
(())((()))
((()()))()
((()()()))
()()(())()

10 rows selected.

rtrim(ltrim(..., ')'), '(')

SQL> with t(id, str) as
  2   (select 1, '(()(()' from dual union all
  3    select 2, '((()()((())(()' from dual union all
  4    select 3, '((()))))))(()' from dual union all
  5    select 4, ')))()(((' from dual union all
  6    select 5, '(()))))(((())((()())())((' from dual),
  7  rec(lvl, id, str, prev) as
  8   (select 1, id, str, ' '
  9      from t
 10    union all
 11    select lvl + 1, id, regexp_replace(str, '\((#*)\)', '#\1#'), str
 12      from rec
 13     where str <> prev)
 14  select *
 15    from (select id, max(str) keep(dense_rank first order by lvl desc) str_mod from rec group by id)
 16    join t using (id)
 17   cross apply (select listagg(decode(substr(str_mod, rownum, 1), '#',
 18                                      substr(str, rownum, 1))) within group(order by level) as str_fixed
 19                  from dual
 20                connect by rownum <= length(str));

        ID STR_MOD                        STR                            STR_FIXED
---------- ------------------------------ ------------------------------ --------------------
         1 (##(##                         (()(()                         ()()
         2 ((####(####(##                 ((()()((())(()                 ()()(())()
         3 ######))))(##                  ((()))))))(()                  ((()))()
         4 )))##(((                       )))()(((                       ()
         5 ####)))((##############((      (()))))(((())((()())())((      (())(())((()())())