Topic on Talk:Atomic Heart
Not sure why FG isn't a target for using DLSS suddenly - you can use it with native res for a "free" performance boost and the IQ impact is arguably even less noticeable than from using SR.
DLSS 3.1 doesn't exist either. There's DLSS Super Resolution SDK v3.1 (your link is for that) but this isn't the same as "DLSS 3.1" - which presumably would be an upgrade over "DLSS 3" as a whole, not just a new version of SR SDK.
I'm not even sure that there will be DLSS 3.1 tbh as at this point Nvidia seems content on providing upgrades to DLSS 3 components (SR, FG, Reflex) without bumping the DLSS 3 package version at all. I expect DLSS 3 to be just DLSS 3 and then maybe there will appear DLSS 4 or something.