Sims appear to be grainy/pixelated?

AThirstyMonster  I'm not totally sure I can help with this, but if you're up for experimenting, please make a copy of GraphicsRules.sgr, in [install location]\The Sims 4\Game\Bin.  Place it in ConfigOverride inside the user folder the game is reading.  Please check that it's the right folder; here's how:

https://sims4.crinrict.com/eng/2018/07/how-to-find-your-user-folder/

The idea is that you can experiment on this copy of GraphicsRules, in ConfigOverride, and trash it if an edit goes badly or you want to revert to default settings.   Please understand that I don't know exactly how changing these settings will affect your game, so this should be considered completely experimental.  At worst, however, the game crashes and you delete the copy of GraphicsRules you edited and you're back to normal.

Open this file, search for option SimQuality, and you'll see a bunch of values for the various Sim Quality settings.  Under setting $VeryHigh, set CASSimTextureSize to 4096 rather than its current 2048.  Immediately above that, set the first value for RenderSimTextureSizes to 4096 as well.  Try just these two settings first.

If you don't get the effects you want, look at this section just below the one you were working with:

if ($vMemoryLevel < $vMemoryLevelHigh or $ramLevel < $ramLevelHigh)
            prop $ConfigGroup SimCacheSizeLimit 200
        elseif ($ramLevel == $ramLevelHigh)
            prop $ConfigGroup SimCacheSizeLimit 350
        else
            prop $ConfigGroup SimCacheSizeLimit 512

Change that last 512 to 1024 , but don't change anything else.  (The other settings shouldn't apply to you because your computer's RAM is rated Uber.

Please let me know whether you notice any changes at all, good or bad.  We can try messing with some other settings too, but I'd rather know the effects of one at a time.  And frankly, I'm not picky enough about my sims' appearances to be a proper guinea pig here—I just don't have the eye for detail.