I know you've been quoted a million times but boy oh boy. What a ridiculous post.
That only happens when the game is rendering two different simultaneous scenes. Aaand it's just the worst it drops to. Meaning that in those scenes are not always 900p.
The rest of the game is 4K. Smh.
According to the video the game averages 1440p in non-spilt screen scenarios on Series X and 900p on Series S (7:54). So not a locked 4k.
Anyway, interested to try this out on PC. I think I'm just going to lock it to 30 fps and crank the graphics as far as they'll go. It's such a slow-paced game so 30 fps shouldn't be too bad.