These are my settings on the SX try them out & see if it cleans up your image.
Resolution mode is definitely the cleanest picture even over visual mode.
Turn down sharpness in your TV settings, not needed nowadays for 4k gaming or tv streaming even at 1440p & your TV does a good job of up scaling hd content from tv programs, it's an old tv setting that's not needed anymore.
Set your HDR settings correctly, I think mine is about 20 clicks from the left until the squares match also my in game gamma is set at 50 not the default 100.
Virtual mirror is cleaner than cockpit mirrors so turn them off if you wish.
Post processing effects on, it very subtly smooths out the images because it takes away a bit of brightness/saturation shimmer.
Bloom off, because this adds a lot of shimmering around lights & reflections on cars & object around the track.
Turn off heat haze again shimmering.
Turn off crepuscular rays, sorry on console they look like **** far to blocky.
Turn off camera shake, all this does is shake the whole image about unnecessarily.
Personal choice but I don't use any camera effects, no camera leaning, no look to apex, no geforce effect, nothing, not saying it makes a difference but the less my camera moves in regards to my actual car movement keeps things clean & clear for me.
If using helmet cam instead of cockpit cam turn off show helmet effect as you're affectively looking through two screens also it muffles the sound to mimic wearing a helmet.
The game looks slightly cleaner using external cam, bonnet cam comes in handy when you can't see through a cracked windscreen.
Rain drops & screen dirt only effect camera outside of cockpit so do as you wish.
Worst case scenario if it still looks terrible just use a weather effect that doesn't cause light effect shimmering like clear or light cloud, use heavy cloud, overcast, light fog or hazy instead.
Worst worst case which I don't use or recommend is turn on the depth of field effect so it blurs your surrounding image as you drive faster leaving your focal point clear.
Trust me during a full time cycle on any track there will be times where this game will look absolutely gorgeous then absolutely crap no matter what you do, it all depends on a certain time, during a certain weather cycle, at a certain point on track.
Either way I think PC2 is brilliant & it's still the only game I actually own on my SX.