if you read this artickel about the Co-Op splitscreen drop you know that the last 20% left was something there never cant compleet at all since the game engine not wane let then do it since there was a lot of game breaking problems it has make that there have to scrap it.
https://gamerant.com/halo-infinite-split-screen-co-op-canceled-why/
and this artickel you read what a developer from 343 is telling and is explaning why there have drop it.
and its also something to be told that there never will be a split screen Co-Op campaign coming any more.