Welcome to the new age of a.i. ^-^

You're welcome!

ask chatGPT or an a.i.

I don't know what you mean by "reduces to", but this:

())(()))
   ^^^^ 

is the longest balanced bracket substring. Whereas ()(()) is not even a substring of the given string.

AFAIK:
"())(()))" the case at hand
"())  (()))" seperated into contained groups
so the second group has a length of 4