In such a case, this method alone won’t be enough. If the last backup was days, weeks or even months ago, then there would still be lost data despite the restoring.If you have created Time Machine backup before macOS Big Sur upgrade or downgrade, you can restore lost or missing data from the backup.As a result, it’s possible to easily recover documents, apps, music, photos and other data missing after Mac update. Time Machine is a backup utility built-in to macOS, allowing you to back up your entire Mac.
If you have complaints like “I updated my Mac and lost everything” or “Mac update deleted everything”, the best possible solution is to get things back from Time Machine backup. Restore lost files after Mac update from Time Machine backup
Before upgrading to macOS Big Sur or Catalina, please be aware of possible data loss and try to minimize the possibility. Note: Before you get all your lost data back, it’s recommended not to put new data to your Mac in case that the lost files would be overwritten by new data.