Following yesterday's rollout of the Fallout 4 next-gen update, we noted how the Quality Mode on Xbox Series X and S appeared to run at a very smooth 60FPS, despite Bethesda stating that it would only support up to 30/40FPS.
Well, it looks like the reason has been revealed. According to Digital Foundry's tests so far, Quality Mode simply isn't working on Xbox consoles right now, with the game sticking to Performance Mode no matter what you choose.
Since this tweet, a bunch of PS5 owners have chipped in to say they do see a difference between Quality Mode and Performance Mode, so it seems that Xbox is the only platform with this bug at the moment.
Hopefully Bethesda is already well aware of this and working on a quick fix, but in the meantime, we're basically stuck with Performance Mode on Xbox for the time being. That's not a terrible thing though - at least it's 60FPS!