How do I install macOS on external drive? I want o install Big Sur on an external drive, but downloading Big Sur from Mac App Store only wants to install the OS on the internal drive. How do I get hold of a "ordinary" dmg-file?
Mac mini, macOS 12.0
When you see the start install screen that shows your internal drive select "show all drives" or it will only show the internal drive.
Just pick the drive you want to install it on when it asks.
If it doesn’t offer that drive, make sure it is formatted with APFS and a GUID Partition map.
It may also need to update the firmware on the Mac. Which could be driving it to only use the internal drive—not really sure about that.
There isn’t any other installer, but perhaps it is a “stub” installer issue. You could try moving the current installer to an external drive, then run this in Terminal:
softwareupdate —-fetch-full-installer —-full-installer-version 11.6
Then the drive must not be formatted correctly. I would erase and start over and be sure it is formatted to APFS.
If your Mac has a T2 chip, you may have to allow booting from an external drive. See: About Startup Security Utility - Apple Support
and i should add, i still use my internal drive as my main startup drive. when i want to use one of the other macOSes, i hold the "option" key while starting up until i see the screen where i choose which drive i want to boot into.
It only show the internal drive.
The external drive was formatted Mac OS Extended.
One might have issues since the profile attached to the question is showing Mac mini, macOS 12.0 Beta Monterey
when i set up my external boot drives i followed the instructions in this informative and well written user tip:
How to Setup and Use an External SSD as your Startup Disk - User Tip
How do I install macOS on external drive
