Sims 3 Glitches / "Pets" Problems (Mac)

@stephmcca  Pets is the most graphically demanding of all Sims 3 packs, and it almost requires a dedicated graphics card to run properly.  Your integrated Intel 6100 isn't built to be able to handle the load that Pets places on it.  So it's unsurprising you'd be seeing these issues.  Seasons is the second most demanding pack, although its impact is more variable, i.e. rain and snow are harder on a graphics card than a sunny day.

Additionally, the Mac version of Sims 3 can only use 2 GB memory at a time, which may be causing some of the crashes as well.  (It's difficult to tell from your description.)  The more packs you add, the more RAM the game uses.  Longer-running saves will also require more memory than new ones, as will larger households.  So you can easily get to a point where an existing save is almost unplayable even without being corrupt.

If your game is crashing even with no mods or cc, then there's unfortunately not a whole lot you can do, other than maybe uninstall Pets.  If you're willing to play without it, that's probably the best approach, at least for now.  Be sure to remove all the hidden library files as well:

https://bluebellflora.com/manually-uninstalling-an-expansion-or-stuff-pack-in-the-sims-3-for-mac/

At some point, hopefully soon, the 64-bit-compatible version of Sims 3 will be released for macOS.  We have no idea what it will look like, but what little we've heard suggests that the game is being significantly reworked.  It's possible, although maybe not likely, that Pets will run better in the new version than in the old one.  At the very least, it might be worth trying when that new version does show up.