Art is both subjective and objective, in a sense. In fact, they’re two different, respective sides to art. Kinda like how there are the light and dark sides of the Force in Star Wars.
The subjective side is about how it makes the viewer feel, emotionally. For example, whether a certain character annoys you or not, or whether the soundtrack of a film makes you really emotional… those are subjective.
I can understand what people mean when they say that art is objective. They’re referring to things that actually happen in the movie, such as Rey defeating Palpatine in The Rise of Skywalker. Plot holes, inconsistencies, contrivances, and other related things are based on things that actually happen in the film, and thus are objective.
Obviously, whether plot holes and the other stuff I’ve listed aren’t “objectively bad”, they’re just things that exist in the movie. They’re “subjectively bad” in the sense that they tend to ruin people’s enjoyment of the movie, but it doesn’t change the fact that the movie is “objectively imperfect” or “objectively incoherent”.