Which manga of the current state of the Jump with less of 300 chapters ( so everyone started from My Hero Accademia ) will reach and surpass the 400th chapter according to you ?
If they let Tabata accomplish his desire,which maybe can end up not happening, probably Black Clover, but i think that only this one, would go for 400 chapters.
I still uncertain about Jujutsu, i think it It all depends on how the current arc will turns out.
Chainsaw-man, given the last developments and the spoiler of the last chapters, seems to be heading towards the final act. The same can be said about Boku no Hero, i think the last arc could last until chapter 350 or 380, but i don't think the work has enough "energy", to go for more. There's no way a villain could top present one, be it in level of power or relevance, and since Boku no hero is about Izuku, and not the world around him, there's little reasons to expand the world.
We have the newbies, but it's still to early to judge them in this aspect, a lot of them could go for 400 or end before reaching 100, but by now there's no means to precisely judge this, at least in my view.