As has been said already, this is definitley a problem with the world updates and photogrammetry. I did a completely fresh install today and in the base game with no world updates my framerates were absolutely fine at around 60fps.
As I installed each world update and tested in game the framerate got progressively worse until it reached unplayable speeds of around 15-20fps on the ground. As with a lot of people here, the moment I take off the framerate shoots back up to a stable 60+ fps.
Turning off photogrammetry with the world updates installed also restores the framerate to a stable 60fps.