Red World Bug

I've tried searching for fixes for this and the only ones I found were many years old so hopefully there's an easier fix? Anyway, some of my worlds in the Sims 3 are completely red, but operable. Sunset Valley and Hidden Springs are both plagued by this, but Starlight Shores and Monte Vista aren't. This happened after my pathetic attempt at trying to install mods. (I've never use mods for anything before)

I did tamper with the resource.cfg file, I didn't change anything but I had to download it or something if that has anything to do with it... I installed the weapons system mod, but it's very popular so I don't think it's a defective mod. I did have the Sims 3 Mod Manager but I completely deleted and uninstalled it, because apparently this has caused this bug before. My graphics card is top of the line and I can run and play anything...so it's not my graphics card.

If the only solution is to reinstall The Sims 3 what is the procedure? And if you could explain it to me as if I'm 10. xD. I honestly do not know all this "back up your files" and I don't want to risk thinking I did it right and find out I didn't back them up and losing everything. I also was told doing this means I have to reinstall every single content update/game patch singularly which I straight up am not doing...I don't got 100 hours to sit here.

If you can help me get my game back to normal I got a bit of left over Sim Points I can offer you.