If you have FSR 4 upscaling enabled and seeing odd shimmering near the edges of the screen, then it is likely due to chromatic aberration.
To check if you have this issue, go to an area with a few trees such as Lostwing, or even near the exit of Caer Norvent where I found it most apparent. Then, position your camera so that the trees reach the edges of the screen. You should see excessive shimmering. Try disabling chromatic aberration in the graphics settings. The trees should now be relatively stable when still, and quite stable during movement, as expected. I believe this is due to the upscaling pass being applied after the chromatic aberration filter, which is weird since it is a post-process effect so you would assume it would come after.