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How can I install macOS version 11.2.3 (Build 20D91) (or older version of Big Sur, such as the one it came with) on a partition or volume (that I've already created) my M1 Mac?

I've tried multiple ways and nothing is working, and Apple hasn't been helpful so far, by phone or at the Genius Bar.

I'm astonished I get 0 hits with this google search: https://www.google.com/search?q=%22Restore+image+for+macOS+version%22+11.2.3+(Build+20D91)+%22is+not+supported+on+this+machine%22

Some background: The M1 Mac was ordered directly from Apple and arrived March 31, 2021, and so certainly can't have come with a version newer than 11.2.3. 11.2.3 was the latest production version of macOS on March 31, 2021.

I found an interesting clue!

nvram -p says: ota-original-base-os-version 21G83

This is odd; this is way off - this is a very recent version of macOS - 12.5.1, as in UniversalMac_12.5.1_21G83_Restore.ipsw

Does anyone have any idea if it makes sense to change this setting?

I tried nvram ota-original-base-os-version=20D91 but it hasn't made a difference.

*My M1 Mac is happy to download Big Sur using the link Glyph provided, unlike his: But this is newer than the version I want to install anyway. Screenshot of the Software Update preferences panel downloading Big Sur

I wonder what the cause for this difference is; could be a lead.

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3 Answers 3

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Downgrading an Apple Silicon Mac is generally not possible. You need to revive or restore it from another Mac to ensure the firmware matches the OS and the installer.

I'm assuming you have a very, very good reason to attempt to dual boot or run on hardware this OS only. If not, you would be better suited with virtualization to run the "older" OS and let your Mac ride the firmer, recovery OS, macOS normal upgrade train.

There's lots of good writing on the internet as people upgraded to betas, downgraded back to production and more. I haven't seen any that contemplated the nvram or partition scheme as a good plan and most I know of ended up needing to wipe and run one OS at one time on their Apple Silicon Macs. The new filesystem, boot, recovery and T2 / processors make the old way of attempting this not technically sound.

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You will find that virtualization options specifically do not support anything less than Monterey on Apple Silicon (https://kb.parallels.com/en/124223, https://github.com/insidegui/VirtualBuddy/blob/main/README.md, https://docs.getutm.app/guest-support/macos/), due to the absence of the virtualization framework that makes this possible. Virtualization wasn't even allowed until Big Sur https://www.macstadium.com/blog/developers-big-sur-and-vindication and so it was not super well supported on the new hardware.

There were bugs in Big Sur which caused physical damage to the mac, so while these were nominally fixed https://9to5mac.com/2021/02/25/macos-big-sur-11-2-2-usb-c-charger-fix/ it makes sense that apple might be cagier than usual about this particular downgrade. The link from Apple's own download page, https://support.apple.com/en-us/HT211683, to Big Sur won't download for me on any Apple Silicon computer.

Impossible to prove a negative, but I think you're out of luck. It might be useful to know why you want to do this?

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According to @bmike: "You can relax the boot security and bring any OS you please to the hardware - all this is documented in the Apple Platform Security guide and this KB, @WHO'sNoToOldRx4CovidIsMurder"

(Putting this answer here as, even though it doesn't work for me, even with Genius Bar help, it's the documented answer.)

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