"Beauty" is a romanticized word, so I prefer "attractiveness", which is measurable. Extreme attractiveness is not subjective. It's intersubjective.

Something is purely subjective when "good" or "bad" is entirely contingent on what you think about some thing and there is no common degree of good/bad among people who also evaluate that thing subjectively.

If I poll preferences for female body types I'm going to get a good deal of variance, especially with respect to what is 'ideal', but there's going to be a dominant pattern nonetheless, i.e. shared preferences for what is a 3/10, 4/10, and so on. Hotornot uses this system, and while no one really exceeds 7.5/10 and no one goes below 3/10, there's still marked differences between the two, and if you recalibrate so that 7.5/10 = 10 and 3/10 = 0, then you can develop a strong 1/10 system that, while not objective, hits the mark most of the time.

The 1-10 system has its flaws because a lot of people vote with meta-desires; they want someone to want some person, so they might rate them 6/10 instead of 3/10 -- not enough to indicate they want that person but enough to raise their rating. Conversely the voter might have some value system that punishes arrogance, so if someone who would normally be 10/10 comes off as too arrogant they might want to discourage this behavior and rate a person 7/10 to discourage open discussion of that person's strengths. (I think this is a weird definition of 'arrogance', but a lot of people do think this way.)

You can get around this by using the Condorcet Method, which has been used for purposes as esoteric and difficult as rating post-WWII Anglophone philosophers by importance. Hotornot halfway does this insofar as you are required to swipe "yes" or "no" on a person, but Hotornot assumes that if you vote "yes" you will actually talk to this person, so people who look attractive but 'intimidating' might not get votes for example. OKCupid uses this method to determine facial attractiveness via their "My Best Face" feature, though it's less popular now. You choose which of two people you'd prefer, and this bumps you up against a more attractive person until your position stabilizes. In spite of this, OKCupid's system is still vulnerable to metadesire variables -- i.e. by voting someone might think they are legitimizing someone's personality traits and they don't want other people to want those traits, so they vote a less attractive person instead.

Regardless, if you used some kind of Condorcet system for very neutrally-posed photos (i.e. everyone wore a generic black t-shirt then took a headshot, or everyone wore generic underwear and had a full-body shot) you would most certainly get to some kind of intersubjective verifiability.

It's important to remember that intersubjective verifiability if applied to things that don't have physical correspondents (i.e. your body) can produce some absurd results but nonetheless, there is definitely a dominant and consistent idea of 'extremely attractive' that isn't going to go away.

The idea that you are beautiful to yourself is tenuous because it has to use other people as a reference, because the concept of attractiveness is an inherently social concept and the very word refers to other entities (attracting things); the closest you could get to self-attraction is pseudosocial attraction, i.e. projecting how attractive you find yourself to an imaginary society of people who think exactly like you. Even the act of looking in a mirror is encountering yourself in the way you'd encounter another person. If you were a society of one and lived out in the wilderness without a way of seeing your reflection and had never met another human being, you wouldn't even have a concept of attractiveness. Your body would be solely functional and the very idea of beauty would be meaningless to you without other people to legitimize it.

So, in essence, beauty is intersubjective; if it were entirely subjective, it wouldn't be beauty, but something else, because the very concept depends on intersubjective validity to give the construct weight. If you succeeded in making everyone agree that everyone is beautiful, then you would just find some other term take the place of "very intersubjectively attractive" because the phenomenon of agreed-upon attractiveness wouldn't go away.