Well, the good news is that EA is currently working on updating the Sims 3 so that it is 64-bit and Metal-compatible. So, it should (theoretically) be able to work if:
The bad news is that there is no official timeframe when this should be released. I'm not thrilled about that uncertainty either, but if you can't get a refund, then at least take heart that it's currently being worked on. Which isn't bad for a game that's over a decade old.
The lesson that we should all take from this is "No Half Measures". I mean, sure, Apple does change up a few things that do wind up... killing older apps. The latest update of MacOS killed support for 32-bit apps. Hell, the next one might kill support for games that are running on OpenGL and not Metal. They've done this before, with removing Rosetta (which removed support for Mac apps created before they started using Intel chipsets) and Classic Mode. But The Sims 3 is... special. You see, it uses this third party library called Cider and, well, it is awful. In fact, it could be blamed for why The Sims 3 can't even use all the memory on your computer (which is actually a problem). The Maxis team took a half measure here, and as a result, they created a less stable game that was less capable to stand the test of time.
That's why it's taking so much longer to update it.
