The rain/snow appears to fall inside buildings no matter how far I zoom in or position the camera. It does not accumulate, nor do my sims react to it.

In searching for a solution I found a social media post about turning off advanced rendering. That DID fix the issue, but it created a lot of graphical unpleasantness so I ended up turning it back on. Is there another way to fix it, so I can leave advanced rendering on?

Of note, this only started happening with a recent computer upgrade. My old card was an rx 580 4gb paired with an r5 2600, my new card is a 6700xt paired with a 5600x3d.

UPDATE: My problem had nothing to do with shadows, but I was able to fix the issue by following the steps here.

The fix: I went into GraphicsRules.sgr (in game/bin). There was only one instance of "RenderShadowMode 1" in my file. I changed the 1 to a 2. For reasons beyond my understanding, this fixed everything.

I know this isn't helpful, but I have this same exact issue. So hopefully a resolution can be found on this. I had to turn it back on too because of the graphical issues it caused when I turned it off.

This is definitely an AMD driver issue, because I have had it from time to time as well on my Ryzen 6400.

The first thing I would do is make sure to launch the game using Adrenalin Edition instead of the shortcut on your desktop.

The second thing I'd do is to either make sure to update your graphics driver or, ironically, to roll it back to the previous driver when the game was working.

Launching through AMD just brings up the sims launcher. Is that okay, or do I need to find a way to bypass it?

I know that you solved the issue, but I may as well answer, anyway. There are two exe files for Sims 3, one for the launcher and one for the actual game. You need to manually add TS3W.exe instead of TS3.exe.