Ok, let's do one more search in Terminal for specific saves:
find / -type f -name "*.save*" 2>/dev/null
If that doesn't yield any good results then maybe look in any backups you have? Have you used any 3rd party apps to clear out files on your Mac?
I ran the new terminal search attached a screenshot below. Looks like it pulls up files with "save" other than Sims files but if you see anything I don't, definitely let me know.
Unfortunately, I have no backups to pull from. It's silly because I keep all my files on externals so I never worry about losing data, but The Sims is the only game I play on my laptop so I just didn't think about it since I've never had this issue. Lesson learned haha.
I have used third party software to clear out temporary files in the past (CleanMyMac free version), but I think that was over a year ago and it didn't delete my saves then. I don't think I have run a cleaning it since the last time I played Sims 4 because I dislike the cleaning software and never upgraded to a paid version. It's possible it could have been run inadvertently, but unlikely. The Sims 4 update was the only thing I know for sure that could impact the files, so I don't know.
