HII I’m very new to forums and forum etiquette so pls don’t kill me if I do anything wrong, apologies in advance.
So, one day I had decided to change the texture detail in my game to ‘medium’ just to see what it would look like.
I opened CAS, and lo and behold I see this: https://ibb.co/whhkYQyp

(Btw, it was only the teenage age that does this.)
I went out of CAS, and went into a lot with a already made family and it did
the same thing: https://ibb.co/HprXGbbf (image of what I had mentioned)

I backed up my game and removed the Downloads folder and opened my game.
It did the exact same thing.
I tested it in every neighborhood, with every skintone, and it did the same thing.
I tested it with the downloads folder back in and it did the same thing too, however,
with *Custom skintones* it wouldn’t happen.
So, that being said, it’s clearly an issue with the Basegame skins.

Notes:
- I already made that the main category, but I’m using Legacy Collection.
- This doesn’t happen with the Zombie skin, Or the mannequin skin, but it DOES with the alien skin unfortunately
- For *male teens* it’s the whole body but eyes and hair that turns white, but for *women* their faces are…fine. : https://ibb.co/yn8wHwQn
I don’t NEED to have my texture detail up, my game is perfectly playable!!
But I just want to see how I could fix it.
Thank you for reading this

Have you tried deleting the cache files? If it's just the game momentarily glitching, deleting the files should help, Especially if you've used any sort of default replacement, removed CC sims were using, or - potentially in your case, switching between settings.
The black text/white background usually happens when the game can't find the resources, or have stored old data in the cache files. It's more common to see this issue if you remove items from the downloads folder and sims were wearing them ingame. If this is the issue, it can be fixed by deleting the cache files, or by taking the sim to a mirror.

Have you deleted anything ingame before this happened?
There's a chance deleting texture-referenced items referenced to maxis items can delete or change resources in the original files. If that happens, the afected items/sims can end up looking like this. Deleting such items should always be done from the Downloads folder, just to be on the safe side.

The next you can try is to pull your savefiles (or rename the "Sims 2 Legacy" folder to "Sims 2 Legacy OLD" or some such) and let the files regenerate. Then test to see if the issues happen with new savefiles.

If deleting the cache files or taking sims to a mirror doesn't work, or if it happens to newly made sims in CAS, and regenerating savefiles has no effect, it could be caused by a borked install, possibly by some issues with one or more files.
You may want to try reinstalling/fixing the game via Steam (or whichever other provider you're using).
Make sure to backup your game first (savefiles and downloads sometimes get deleted, other times not).

First things first, no I…kinda didn’t even think about cache files. I feel INSANELY silly that I didn’t even think abt doing that oh my goodness I am sorry.

Secondly, I didn’t delete any CC before this had happened, on the contrary, actually. I had downloaded a bunch of new CC; it was mostly hair, all of which with original meshes.
And I usually delete things via the Downloads folder, not in-game, just because I know it’s risky.
I think I’ve only deleted things that way like, once, and I don’t even think I’ve downloaded any replacements of basegame stuff.
And also, since you mentioned it, I hadn’t deleted any CC that a sim was wearing at the time.

You said in the last paragraph “If it happens to newly made sims in CAS,”
which is exactly how I saw the issue for the first time. It WAS in CAS.
(I don’t know if it will load still, but the first image I linked was taken in create a sim.)
The inciting incident was this: I changed the texture detail in my custom hood,
and went to make a family. I made a teenage sim and then that’s when I saw our said issue.

So yeah, I don’t have my computer near me at the moment, but when I do I’ll try some of the things you recommended.
Thank you very much for your help thus far!!!

Another thing - some antivirus/antimalware programs can mistakenly flag TS2 install files as malware (false positives). You may want to check the quarantine, and also make sure to exclude the TS2 install files in the settings.

But the textures showing up wrong could easily just be borked cache files, so try that one first of all. A lot of TS2 items, especially CC, need the Texture setting to be on high to show properly (some can even show the wrong texture with the lower setting), so when you go from the low to high setting after the items were introduced in the game, that could potentially cause this bug. It's a weird one, though - shouldn't happen.