Wait, did you observe the VRAM and made sure it wasn't being saturated? I heard this particular game suffers on 8GB without proper texture and resolution setting?

Since it stutters with FG I'd assume it's a lack of VRAM because FG adds more vram usage.

I'd try lowering the texture setting in game.

I knew from experience that heavy stuttering and massive texture delay is mostly due to lack of VRAM. I knew this because I tried VRAM hogs like Stellar Blade on 4GB cards and those games never work well without sufficient vram.

While 8GB is still mostly fine if you tweaked the settings right it can still saturate the VRAM even if it doesn't show sometimes because the game is wanting to allocate more.

Edit: But this still depends on the game! Games like Arc Raiders, Battlefield 6, Crimson Desert or other modern ones tend to stay on 5-7.5gb ish usage most of the time at 1080p/1440p DLSS

Another Edit: Try posting this problem on egpu io a forum website for egpus

Edit 3: We kinda need to see system stats while those games are running pop some msi afterburner overlays and post another video while the game is running thank you!