Everything has an objective truth. Opinions are just misinterpretations of that objective truth. If you like a song, it doesn’t mean it’s a good song. If you think someone’s attractive, it doesn’t mean they are. If you believe in something, it doesn’t mean it’s true. You may easily be delusional.
For everything you think is subjective, there is an objective answer. Just because the answer may be extremely difficult to find, this doesn’t mean it doesn’t exist. I will give some examples.
It is very common for humans to disagree upon the attractiveness of another human. But physical beauty is all a reflection of genetics. The most beautiful people are those who have the best genes. They are often healthier and smarter than most other people. But nobody has a perfect genetic makeup, so just because someone is attractive, doesn’t mean they’re not dumb. It might just be that they have a family history of really good health. And there are very often smart, ugly people as well. This is because they’re lacking in other areas. Maybe they have all sorts of genetic diseases in their genes.
For art, there is also an objective beauty. The beauty of art is a reflection of honesty and depth. The deeper we can empathize with the artist through her art, the better the art is. But it is important to distinguish between art and entertainment. Good entertainment may not be art at all. Action movies like Indiana Jones for example, are entertainment for the masses, but they do not qualify the least bit as art. Art is about expressing what’s within, while entertainment is about affecting the audience.
There are plenty of other examples of things that are seen as subjective, but in reality are objective. But there’s no reason to list them all. If you have the brains, go ahead and figure it out for yourself. If you put in enough thought, you can find the objective truth for anything.