I'm bringing this thread back to the top since my daughter has the same problem. She has the Xbox Series S and downloaded and played the game for a couple of hours. It saved just fine. The next time she loaded it, it said it was corrupt and wouldn't load.
I wanted to share for the benefit of anybody having this problem what we did for a workaround (and I say workaround since it doesn't actually fix the issue, it just moves it out of the way).
During testing, we found that a new game would also be corrupt a few minutes. If she played longer than that, every save file, even a new one, was corrupt. We followed the guidance and uninstalled and reinstalled the game, cleared the cache, etc. The problem persisted and we again noticed it happened after a few minutes.
So I started fiddling around with the saved games and noticed that there was an "autosave" file that kept get overwritten. That autosave was named for her very first city and it seemed the game was trying to load it instead of the save file she was selecting. On a hunch, we disabled autosave and the game saves just fine now, no matter how long she plays. It appears that the default is to autosave every 10 minutes and somehow, the rewriting over and over corrupts the autosave file. Turning auto-save off seems to get past it.
One thing I still don't understand. I'm more of a Playstation guy and on that platform, it is possible for me to discreetly manage local saves vs. cloud saves. For the life of me, I cannot find the ability to do that on Xbox. The reason I ask is because she was able to delete all of her corrupted manual saves by using the in-game interface. However, we did "uninstall all" on the game - twice - and every time we reinstall it, that original autosave file comes back. It appears the game is pulling it from the cloud and I can't find it any way to permanently get rid of it. It's also not deletable in-game - the "delete" option doesn't even appear.
In summary, here's what we did to work around the issue:
1. Uninstall the game completely.
2. Clear the cache by unplugging the box for a few minutes.
3. Reinstall the game.
4. Start the game and IMMEDIATELY disable auto saving (do NOT start a new city without disabling it first)
5. Enjoy the game but make sure to SAVE OFTEN because the game won't do it for you anymore.