My Hero Academia focuses heavily on that universe's power system, Quirks, and the main series gives a lot of attention to how they work and their inner mechanics, which is something that the movies usually struggle with. That is something that is quite telling in the 2024 movie, You're Next!, since the film itself has a time constraint because of the medium so the new characters' Quirk cannot be fully explored.
The best example of this trend is the character of Dark Might, whose alchemy Quirk might be one of the most unique and versatile in the My Hero Academia universe but is never given the time to study its mechanics. There are other examples across the films, especially when it combines that with the expanding world-building that leaves fans wanting more.
Disclaimer: This article contains spoilers from the manga/anime and reflects the opinions of the writer.
Explaining the limitations of Quirks in the My Hero Academia films

It is easy to see why Studio Bones and the team responsible for the movies won't have much time to explain the characters' Quirks in these films, as these productions typically last no more than three hours. Consequently, when introducing new characters, a plot, and action sequences, along with giving the established cast their moment to shine, it makes sense that some abilities remain underdeveloped.
As mentioned earlier, the case of Dark Might is the most obvious one since it shows his ability to use Alchemy, and the full extent of this Quirk is quite large. While this ability, powered up by Anna Scervino, was enough to fight Izuku "Deku" Midoriya, Katsuki Bakugo, and Shoto Todoroki on his own, it was also somewhat underexplained, resulting in a lot of frustration for the fans.
An underling of Dark Might's, Deborah Gollini, also one of the most powerful Quirks in the franchise, Day Dream, which allows her to make people fall unconscious and have dreams of what they honestly desire. She can only use it on one person, but Anna's own Quirk gives her a boost that makes her quite powerful, even though the film never explores this.
More examples of this

Another prominent example of that in the My Hero Academia movies is the character of Nine, whose Weather Manipulation Quirk takes a massive toll on his body, but that is mainly used to explain his connection with All For One. However, the full extent of a Quirk that can control the weather is something that could have a lot of exploration in a longer story.
It makes sense, though, that Studio Bones wouldn't be able to fully explore every single idea that is introduced in the movies, since time constraints and connections with the main series create those issues. It is a mechanic of the film medium, and fans need to accept that variable, all things considered.
Final thoughts
The My Hero Academia films were always going to have issues with the Quirks they introduce because they never got the time to be fully fleshed out. It is a running issue when making anime movies, and not much can be expected of Studio Bones beyond this situation.
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