Beauty is a result of having a specific feeling whose name is non-existent in English, but exists, at least, in Hebrew.
In Hebrew, the word “beauty” comes from the action of being “beautified”, and that action, as a noun, is also an emotion. In English you can call it “beautifition”, even though no such word officially exists in English.
So everything that is beautiful, in order to be beautiful, it has to make you feel “beautified”, AKA, wondered, awed, fascinated, intrigued and so forth.
Compare it to “disgusting”. Disgusting simply means something or someone that makes someone else, or even themselves, disgusted.
Therefore, technically, beauty is supposedly an action, or to be specific, a reaction. It is a trait that leads someone to a specific reaction, either by behavior, feeling or thinking, depending on the correct definition of the trait.
Because different things and beings make different people react differently, beauty is indeed subjective, even if there are things that we can agree on a collective level that they are indeed beautiful, like there are things that many of us can find disgusting.
I disagree with the affiliation of objectivity with collective agreement. It’s not that a widespread agreement about a subject necessarily makes it true or false. That’s how democracy works, not how logic works. If we are to agree that beyond a locked room there is a tomato, and there isn’t a tomato, would a tomato in that room emerge into existence, just because the majority of us are convinced that there is indeed a tomato beyond the sealed door?
And indeed, collective agreement cannot change the initial, necessary definition of words, like what beauty actually means in Hebrew, for that matter - something that makes you feel beautified, but not is not necessarily beautifying on a universal, absolute degree.