Ok, I uninstalled Origin completely following your instructions very thoroughly and emptied trash before restarting and downloading Origin again. I triple checked all folder locations to make sure Origin was completely removed. Then I downloaded just the basegame. I had the same result of immediate crash.
So I repeated the steps - removing all trace of Origin, reinstall Origin, redownload basegame only. Same thing.
But I think I have noticed a pattern through all of this. The original steps suggested by numerous people to clear the cache or get a clean The Sims 4 folder never worked for me. When removing all traces of Origin & The Sims 4, I deleted my Documents/Electronic Arts folder because I had saved my The Sims 4 folder in 2 separate spots so I could introduce it back in once I can finally get the Sims to load. But after the 2 most recent downloads of The Sims 4 from Origin, no new Documents/Electronic Arts folder was generated. At no point was there a pop up asking for access to the Documents folder, either. It just told me it was going to install the Sims4 to the Applications folder by default. The second time around, I actually changed that location to my Documents folder in an attempt to get a different result.
So it seems like there's a problem with accessing my documents folder overall. But where can I manually grant access to that in the Origin app? I've gone through preferences and Game Properties, disabling Origin In-Game. I don't see any place to grant access to Documents folder.