Big Sur Security Update 11.7 Breaks Time Machine backups

After installing the Big Sur Security Update 11.7, resulting in corruption of the code that updates the Mac for iPhones, I went through procedures to reinstall Big Sur by rebooting using System Recovery. In my efforts to erase and reinstall the System, a Big Sur install reformatted my drive without warning resulting in the complete loss of all user accounts on the drive. After the reinstall, I attempted to use Time Machine to recover my data and found out that Time Machine could not access any of my Time Machine backups under 11.6 and earlier as it could not recognize the format. In fact, the App indicate I had no backups. After hours of effort, I was able to access the backups via Migration Assistant and was able to recover my data. This was verified with an Apple Support Agent screen sharing and seems to be something that Apple Support was unaware of. I then verified it was a 11.7 issue by rebooting my machine using a different drive formatted with 11.6 and the Time Machine backups were accessible by it.

The bottom line of all of this is that MacOS 11.7 changes in Time Machine format results in all Time Machine backups by earlier versions being inaccessible. and the only way to access them is through Migration Assistant unless you have another bootable drive with an earlier version of Big Sur. This also means you are unable to recover individual files from earlier Time Machine backups after installing 11.7.

What did you mean by this?

Otherwise the story sounds as if the likes of or @howardnoakley at may want to hear about it.

When doing the update to MacOS 11 or when reinstalling MacOS after MacOS after 10.13, or 10.14, when first connecting an iPhone to the updated computer MacOS will request to do an update to its system, via a window in the middle of the screen to update the interfacing to the iPhone. This is an internal update for MacOS that only takes a short time to download and install and does not require a reboot. It is not an update to the iPhone. After I updated to 11.7 from 11.6 the window appeared as usual for such an update when plugging in the phone to the computer but either the download froze or failed to complete its update with an error message. This happened after each reboot. After reinstalling the latest version of MacOS 11 (11.7) using System Recovery, the download and install proceeded to work properly as it has always done despite the fact that when speaking to an Apple level 1 Support Agent when the error first occurred, I was incorrectly told that the only way to stop the error message from happening each time I plugged in the iPhone after rebooting or starting the machine was to upgrade the machine to MacOS 12 (Monterey). I chose not to do this as it would have disabled the ability to use my Brother ADS-1500 scanner as Brother has provided no driver update for Monterey compatibility which would have required me to purchase a new scanner to replace it.

I’m sorry the update gave you problems—and I’m glad that apparently, so far, it did not give me problems (but it was an odd experience).

I installed macOS 11.7 earlier today. Time Machine is backing up as I type this, and I entered Time Machine and could see earlier backups. I did not try to restore a file from an earlier backup, but I could see the files and nothing looked different from other times that I entered Time Machine.

My comment was based on a single experience backing up to a real hard drive (spinner) formatted in APFS. The last backup onto this drive worked correctly on 11.6. Additionally, the files are available when my machine is booted from another drive with 11.6 installed. My machine is a MacPro 7.1 2019 Desktop computer.