Install Mac OS on external drive: disk locked I am trying to install Mac OS Big Sur on an external drive (Samsung portable SSD T5 256GB) following the macworld directions. I get to the very last step, however there is a message that the disk is locked and it can't be selected, so can't install macOS on it.

I have previously installed macOS on the drive using restore from backup, but I just want a minimal OS install, not all my stuff from a backup.
I have also tried to select the drive as the boot disk, but get a message that I can't select the drive because &quot;the bless tool was unable to set the current boot disk&quot;.

There is a previous question Disk Locked” macOS reinstall! however I don't think that helps, there's also a post on an Apple discussion forum about the bless tool, but that doesn't help either.
Any ideas on how to rectify this?
Of course after hours of trying, I found an answer soon after I posted.

I connected the external drive
From the app store, I found Big Sur and clicked &quot;Get&quot;. Because I'd already downloaded the installer, it started after a few moments
I clicked continue and accepted the Ts &amp; Cs
When the &quot;select disk to install&quot; came up, only the internal disk was shown so I clicked the &quot;Show all disks&quot; button
The external disk was also shown, so I selected it
A message said the disk couldn't be used as it wasn't APFS with GUID partition map
I backed out of the installer, ran disk utility, erased the disk and formatted it as APFS with GUID
Ran steps 1 to 4 again, this time the install proceeded
20 minutes later I had a bootable external drive.

The above is far simpler than the MacWorld instructions.