Is there a way to repair a corrupted save file?

There isn't anything I can think of to fix the save itself. The game does keep a copy of the last 5 versions of a save if that helps any. To access them, you go to "Load Game" from the main menu. Select your save slot. To the left of the play button is "Recover Save". This opens the list of past save versions. Clicking on any of them copies it to a new save slot with "[Recovered]" appended to the name. From there, you can load it like any other save.

@alad050193 - Try the recovery that @SDPhantomGamer suggested first, it's excellent advice. If you've been dealing with the corruption for a while, you may not have any good auto-saves, though.

Even though you've done the repair and determined the issue only happens on your legacy, you might be able to save your legacy by resetting the game. Follow the instructions for the Mac here: https://help.ea.com/en-us/help/the-sims/the-sims-4/backing-up-and-resetting-the-sims-4/ Once the game is reset, try copying each of the save files one at a time from the backup folder to your main documents folder. Maybe the corruption is in an item or house file that's used in the legacy 🤞

I have a legacy challenge just about to start gen 5, so I feel your pain. In my case, I lost all the files in my saves folder in gen 2 and had to start over. That taught me to do regular backups of my saves, not just using "save as", just in case. Now, before patches or major changes in my game I will back up the entire TS4 folder, and weekly or so I'll copy just the saves folders to another folder on my hard drive as backup. It was a hard lesson to learn. I hope you're able to recover your game. Happy Simming!