External boot to older macOS?

[Roy G Biv]

Has anyone tried booting from external drive on M1 Mac with Big Sur or even an older OS? It appears it is possible:

"In reduced security mode, you can boot any supported version of macOS, even if Apple’s no longer signing it. And if an app or accessory you rely on uses a third-party kernel extension to enable functionality, you’ll need to use this mode."

Apple Silicon Macs will offer new macOS Recovery options, replace Target Disk Mode with Sharing Mode - 9to5Mac

In a new WWDC session video today, Apple has elaborated on the system architecture of the forthcoming Apple Silicon Mac...

9to5mac.com

 

[casperes1996]

You can boot external drives, yes - You cannot boot an OS prior to Big Sur on an M1 Mac because it would not have support for the hardware - Same as you generally can’t boot macOS prior to the make of a given Mac model, external or otherwise