Run Big Sur from an external HDD on M1 Mac

[Hessel89]

Hi there,

I've made a bootable Big Sur installation on an external HDD. I can boot this from my 2017 Macbook Pro but I can't from my M1 Mac. Is it somehow possible to make a bootable Big Sur install on an external HDD? (I know it's possible with Thunderbolt SSDs, but I only have an external HDD at hand)

 

[Apple_Robert]

I don't believe it will work with a platter HDD.

 

[Mike Boreham]

I've made a bootable Big Sur installation on an external HDD. I can boot this from my 2017 Macbook Pro but I can't from my M1 Mac.

An installation made on an Intel Mac will not boot an M1 Mac or vice versa. (But USB install sticks will boot either).

Is it somehow possible to make a bootable Big Sur install on an external HDD?

I just tried installing 11.3.1 onto an APFS partition on an external HDD using Recovery and it worked and booted. The internal was also on 11.3.1 so the external OS was the "same or higher" so this worked without Reduced Startup Security.