Ive just installed it, started a new game and it was juttery for me too. Was on ultra like so maybe thats it, i changed settings but it said reboot game and i couldnt be bothered to to see if it fixed it dropping it one level down. Ill see next time. It was a bit strange tho as last time i played which was yonks ago when vulkan api for it came out, it ran pretty nice as before with my vega 56 it ran terrible due to i think dx11 but when vulkan came up it ran really well. Maybe its just cos of the new start that caused the jittery bits when i was moving around or firing the thing at some rocks for the first time and the game was still caching the gfx into vram or somit maybe.
a lot of reports on steam forum say they also have performance issues after the latest updates, maybe something broke or the gfx have been upped so either need to lower settings or something now i dunno.
I heard a thing about turning tessalation to standard and maybe volumetrics too, ive done that and saved but i need a restart the game, to see if it worked.
Also i had a shader folder full so i deleted those to see if it helped, it did a bit i think.