You could listen to all the experts who say it’s impossible, will make it worse, set you PC on fire, cause mass hysteria, etc. They’re probably right.
I heard the same thing about enabling re-sizable BAR in the game profile. But I tried anyway and it helps when looking quickly side to side. Not so much with FPS when looking straight ahead, though.
So you could get a NVLink bridge and try editing the game profile with nvidia profile inspector. There are many SLI-enabling options in there, and they’re all turned off with the default game profile. See if you can find settings that make an improvement with two linked 3090s. You might be the first to discover something.
I’m not convinced that MS even wants to try. Last thing they need is someone to find that it improves things and then MS marketing has to contend with the press and forums saying that you need dual 3090’s to run VR smoothly.