How to roll your M1 Mac back to Big Sur 11.1

Quite a few users who updated their M1 Macs to Big Sur 11.2 recently are regretting having done so. Those who rely on SoftRAID to access an external RAID system are among the most obvious, as the current release of SoftRAID is incompatible with 11.2, and lost all access to any disk requiring it. If that happens to contain your backups, then your Mac is in trouble.

But no worries: according to many accounts, all you have to do is to restore your internal disk to 11.1 using a snapshot. The only snag with those accounts is that it doesn’t appear to be true. Neither of my updated M1 Macs has any trace of a snapshot of the 11.1 System volume, now that they’ve been updated to 11.2. So what strategies might be open to you if you need to revert to 11.1?

Revert to a System snapshot of 11.1

According to these instructions given by SoftRAID, you can enter 1 True Recovery (1TR) and revert to a previous Time Machine snapshot of 11.1.

To try this, press and hold the Power button until the display shows Loading Startup Options, then release it. This takes you to the Startup Options screen. Select the Options icon, then click Continue underneath it. In the macOS Recovery window select your user icon and click Next. Enter your password in the dialog, select Restore from Time Machine and click Continue. Click Continue in the next window. Time Machine System Restore will then list Restore Sources. To restore from a previous backup, select your backup disk and click Continue. Then select the backup which you wish to restore. To revert to the previous version of macOS, select the last snapshot containing that version, then click Continue. A dialog should then invite you to install that version of macOS, which you would accept. The snapshot should then be restored, and your Mac will reboot from that version of macOS.

However, at present neither the macOS installer nor Time Machine keeps snapshots of the System volume which you can restore using this method. Instead, when you do try to select a Time Machine backup – assuming that one is accessible – you’re told to install macOS instead, which of course will merely deliver 11.2 again.

Boot from an external disk with 11.1

Although I’m not sure how this might help you revert your internal disk to 11.1, it might at least give you a way of restoring access to whatever broke in the update to 11.2. Unfortunately, as I’ll describe in a separate article, once your Mac has been updated to 11.2, it appears impossible to boot it from an external disk with 11.1 installed, presumably because of firmware incompatibility.

If you do try this, you’re likely to find that your Mac gets stuck in a boot loop because of a kernel panic. This is the result of the booter being unable to find IOAESAccelerator, and can only be resolved by shutting down, disconnecting the external disk, starting up in 1TR, and setting it to start up from the internal boot disk again. Your Mac should restart normally, back into 11.2 again.

Download the 11.1 full installer

When Apple released the update to 11.2, it removed all access to the full installer for 11.1. Unless you have a copy saved on an accessible disk, you will thus be unable to obtain 11.1 to create a bootable installer.

Restore in DFU mode

One sure way to restore your M1 Mac to 11.1 is to wipe it completely and restore the firmware and software for 11.1, in DFU mode. To do this, you require another Mac running at least a late version of Catalina, a USB-C or compatible cable to connect the two Macs back to back, and a copy of Apple Configurator 2 installed on the other Mac. The process may appear daunting at first, but it turns out to be relatively quick and simple, provided that you follow Apple’s instructions carefully.

Before attempting this, it’s worth downloading the 11.1 IPSW file, athough Configurator will do that for you if necessary. Mr Macintosh maintains a list of links to available IPSW files which make that straightforward.

If you’re unable to perform a restore in DFU mode, then the only remaining option is to get an Apple Service Provider to do this for you. Unless you’re in an area in which Apple’s stores remain open, that could be far from convenient.

Should you update an M1 Mac?

Currently, the only reliable way to restore an older version of macOS to an M1 Mac is using DFU mode, which inevitably wipes the entire contents of its internal storage. If you can’t or won’t do that, then you should be extremely cautious before installing any further macOS updates. This applies most importantly to those who rely on kernel or system extensions, which are at greatest risk of being disabled when macOS is updated.

Until Apple provides a more accessible way to restore the previous System volume, anyone who can’t wipe their M1 Mac and restore it in DFU mode would be wisest not to install any further updates to macOS.