The steam version and consoles.. have stuttering due to nanite and some other effects.

Still remain unfixed. All version used a older version of UE5.

So does the GOG version still the same version?

I don't know anything about these bugs, but I think you can safely assume that the GOG build does not use a more up-to-date version of the engine than the Steam build.

All I needed to hear. It's the same buggy mess that resides over at STEAM.

I completed the game on Steam and did not encounter any bugs, stuttering, or performance issues of any kind.
I just wanted to point out that it is highly unlikely that the developers have released a more recent version on GOG than on Steam.

Probably system requirements. I should imagine the SR for this game are quite chunky. Amazing that it's here.

You seem to be the only one in the world, mate.

The analysis in this article sounds reasonable. I can confirm the problems described with Unreal Engine 5 from other titles that run on this engine, so I definitely believe that the problems exist and that some people are having issues with them.

But as I said, I haven't had any myself and I doubt I'm the only one. Even in the article you linked to, there are commenters who say they haven't had any problems. I actually think the developer has done a good job of optimizing the game, especially since the article is from October 2024, shortly after the game's release. There have also been a few patches in the meantime.

You are not, in fact, the only person in the world on this. I experienced no issues when I was renting the game on steam for my first go, and starting my second run after being able to buy the game, I continue to experience no such thing.

I'd have to look at the files to confirm this but I would imagine that the same Ultimate Engine Tweaks mod that allows Stalker 2 and Oblivion to run smoothly could also work for SH2 with some slight tweaks.

Removing Nanite helps a lot with the performance. SH2 run to an older version of UE5. Which is why Stutters are so prominent.

Yes! This right here! It seems like such a small thing to remove or alter Lumen but it takes only a few lines of additional code to make it work in other UE5 titles. That kind of programming is way out of my league; I simply state that a mere few lines of code can turn a game engine from nearly unusable to a decent performer on mid-tier hardware.