I’m delighted to report that five months after I wrote that M1 Macs had problems starting up from external disks, Apple has finally fixed Big Su

M1 Macs running Big Sur 11.4 support external disks fully

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2021-05-27 07:30:07

I’m delighted to report that five months after I wrote that M1 Macs had problems starting up from external disks, Apple has finally fixed Big Sur 11.4 so that they now work fully.

If you have an M1 Mac, you should now be able to connect supported storage, such as an SSD, install on it any version of Big Sur from 11.2 onwards, select that in the Startup Disk pane, and boot your Mac from that external disk. The procedure for doing this is exactly as you would expect:

You can then switch between available boot systems using either recoveryOS or the Startup Disk pane. When using those, the first time that you choose a startup disk to boot from you’re likely to be asked to assign it an authorised user. You may also be asked to authenticate up to three times in rapid succession. There may be quite a long pause before your Mac restarts from the chosen boot disk. Once started up using the external system, you’ll be prompted to authenticate to access the Mac’s encrypted internal SSD.

Changing between external boot disks is normally simple and direct using the Startup Disk pane. Changing back to the internal SSD when booted from an external disk usually requires a visit to recoveryOS, where you need to authenticate in Recovery Assistant. After a long pause, once that has been accepted as successful, select the Restart button.