I’m still running Sierra on my 2012 MacMini. I’ve largely stuck to that because I’m running an older version of InDesign and it seems to work well. I’m at a point though where I’m thinking of updating to Mojave but figured I’d do an install of Sierra onto an external usb drive for the rare occasions that I need to work with InDesign.
I used SuperDuper to make a copy of my internal ssd. It shows up as a bootable drive in System preferences but when I attempt to restart using that usb drive I get a circle with line (“Prohibited” icon according to the Apple page on start-up icons) at the end of the process. Any thoughts on the fix?
Running the latest version of Sierra. It’s a powered hard drive formatted as Mac OS extended, journaled, GUID partition. USB connected directly to Mac, no hub.