It wasn’t just a new number that came with Big Sur, finally turning macOS from 10.x to 11, but a new way of thinking about the difference between system files and your own data. In the past, many of us had bootable external drives, regularly updated, that we could use to start up our Macs in a pinch, such as when we had a drive failure or some kind of corruption or other problem that required wiping a disk altogether. We might boot from the drive to keep on working, or use the files on the drive to restore our Mac quickly—a fast copy instead of a system reinstallation.
But it’s a new world: Big Sur resists the ideas of a bootable external backup, though more particularly it resists easily updating an external copy of your startup volume’s system files. In this Mac 911 column, let’s start with an explanation of why that is, so you understand exactly how difficult the task has become, and then proceed to the best new strategy.
Read more at Macworld.com