To reduce further the pop-in of grass specifically, you can add the following at the end of your engine.ini in the [SystemSettings] section :
grass.CullDistanceScale=4.0
groundCover.CullDistanceScale=4.0
groundCover.CullMaxDistance=20000.0
Performance impact seems to be minimal after some inital testing, your mileage might vary though depending on your system.
Credit Steam User : Mac Noslo
More optional tweaks can be added if desired : Full Steam Guide link.
After some testing, this engine.ini file is still necessary to have a proper experience. The fix to the brightness in the patch 1.3 did make the game a bit more darker without it, but still Mexico and snow are still too bright.
You can now use the file as is though, without the addition of the r.EyeAdaptation.LensAttenuation from my previous update.
Now that it seems DLSS is working as intended, ie giving performance boost, I used it for a while and I confirm it seems quite good now.
But while DLSS is taking care of the smoothing and as such the anti-aliasing, I could not find a way to turn off entirely AA in-game, there is just no "off" option.
Still using the engine.ini you can make sure the game does not apply any anti-aliasing by adding this to your engine.ini :
r.DefaultFeature.AntiAliasing=0
Additional tweak you can add into the file to disable the auto-exposure that can cause further annoyance, just open the engine.ini file and add at the end :
r.EyeAdaptation.LensAttenuation=0.45
Credit Steam User : sa1vequick
Edit : not necessary anymore as per WRC patch 1.3.