The basic idea of the problem is that if we have the same number of ')'s and '('s we always can make a regular bracket sequence. The substring constraint doesn't matter: you can even take the whole string as a substring of itself or only leave one element behind if that's not possible. Therefore, the question is simply asking if you can re-order the string's characters in such a way we get a regular bracket sequence, and a regular bracket sequence is only possible when we have the same number of ')'s and '('s.
Every test case is N, since we traverse the string once to ocunt the parenthetical values. The trick is that N can't be maximum per test case (the sum of N is capped to 2 * 10^5), so the time complexity is O(T + N).