The split performance for "next gen" is a pretty major compromise to the ecosystem. The benefit of consoles is the single target you can optimize hard for. Different GPU can be tuned, but different CPU is an issue for demanding loads.
X/S is apparently a big difference. But Xbox requires a game tomrun on both with the same features.
So if Larian wants split screen and only one can handle it, their choice is releasing a bad version on the weaker Xbox, or spending a lot of time trying to make it work.
All because Xbox is in denial about what "next gen" really means.
It HAS to be there due to Microsoft’s multiple requirements, both the X and S both have to be the same game, and Microsoft isn’t going to allow split screen not be in their release as well.
It's slightly slower. It's still not bad (unlike last gen where they came out of the box trash), but it's an extra complication.
If they say they can still do split screen, I'm sure they can, but it's generally something that takes more CPU load, so it's taking extra work to do to their standards.
Larian specifically said they’re working on optimizing for Xbox right now, so it seems like they’re pretty confident in making it happen. They seem like they’ve been pretty on the ball for promised features, so I’m pretty confident it will come out.