I haven't seen the movie but looking at its trailer, it looks like it has a different story but the very same purpose which is deku being the number one hero and controlling one for all. If other anime fans didn't notice this, Kohei Horikoshi (the creator of my hero academia if you didn't know) followed the idea of the trend of rewriting the story of the whole anime but with the same purpose which for me was first done by Akira Toriyama did with his series dragon ball in his movies of dragon ball which many others have followed this ideal too but I've not seen but heard. Anyway, I like these kinda movies and I'm still curious whether that all might looking kinda guy was someone else or young all might which is probably young all might as I've downloaded the my hero academia 2018 ost which had ost of this movie and season 3 and one of them's name was "Y.A.M. Young All Might". I've not heard all of the movies ost's but I think the only new ost made for that movie is Y.A.M.
~yours truly otaku friend Kakorot Skywalker