"This Disk is Locked" Reinstalling macOS
I have a 2017 iMac 27" 5K with a 1TB Fusion Drive.I have always used an external SSD for the boot drive.
Now I am selling it, I am trying to install macOS on the Fusion Drive.
When I boot into Recovery and try to install macOS I'm asked what drive I want to install macOS on. But the "Mac HD" has the message "The Disk is Locked".
So then I exit out of this and select "Disk Utility", I select "Mac HD" then "Erase" but the only options for format are "APFS" and not "Mac OS Extended".
And if I select "APFS" and try to reformat the drive nothing happens.
I really have no idea what to do at this point.
See images.