This much seems plausible: whether something is beautiful doesn't depend on the actual responses that anyone has. It might be that no one has seen the thing. It might be that everyone who's seen it so far doesn't have the discrimination to appreciate it. It may be that no one who's ever been born or even will be born will have that capacity. All of that could be true, and yet the object might still be beautiful. But does that mean that it's beautiful apart from all possible responses?

I don't think so. Does this make sense?

Object X is beautiful, but no sentient creature that the universe could possibly produce would find X beautiful.

I have a bit of trouble understanding what it would mean here to say that X really is beautiful. And if that's right, it suggests (as many philosophers are inclined to think) that whatever exactly beauty may be, it has something to do with the kinds of responses that the right sort of creature would have upon contemplating it. That's not a definition, but it does seem to be a plausible constraint.

Notice that this doesn't make beauty a merely subjective matter. It can be an objective fact that a certain object has the capacity to evoke a certain sort of response in a certain kind of creature. But whatever else we might need to say to provide an account of beauty, it's hard to see how the story could be told without any reference even to hypothetical responses.