Yes, your vote doesn't matter in that case, because you have no information to convey to the system: you have no preference. Only votes which are conveying a preference about how the situation should be handled are useful. There's no reason to distinguish between "I care, but don't have anything to say about the topic" and "I don't care" if you're not even willing to vote based on which candidate talks about the issues you care about, at least as far as elections go.
Write a letter or something.
Ed: In a slightly less snarky sense, your vote really doesn't matter at that point. The point you should participate in the process, if you feel candidates aren't addressing your issues, is way before that. It just requires actual amounts of time and effort to shift platforms, though, and participation beyond checking a box every year/few years.
There is: you don't go to vote.
Not really, no. Especially if it's not clear there's an option to say "idk". Say you care very much but don't know what's best? Does your vote not matter, now? If so, doesn't that make the election wrong? But how do you express that?
There may be an answer to this deep inside some legislature chapter XVI section 16 paragraph b, but if people don't know, does that matter?
Anyway, not saying that was the case for brexit. But "That's just how X works" is typically not the strongest argument. There are a hundred ways to implement a democracy, and they all have their own flaws.