Can someone recommend something like this? Hs setting and an apocalyptic theme ty:)

School Bus Graveyard! You can read it on the Webtoon app. It's super good!!

Otherwise there's also Night of Shadows. Or Mouryou No Yurikago, from the author of Erased. I found the manga good but beware there's ecchi (like panty shots).

Apocalyptic but not in HS with still a young cast there's Rebirth. And with a young adult cast there's Paradise on Earth.

I’d be shocked if this wasn’t heavily based on Floating Classroom.

…ah, that was an elementary school setting though, IIRC.

TRY NIGHT OF SHADOWS.

(づ￣ ³￣)づ thank youu