Asked on Super User by Bayside, 1 year ago. No reply there for at least a week.
Why does my iMac (Retina 5K, 27-inch, Late 2014), running macOS Big Sur 11.6, not boot from external USB drive with an older macOS?
Why does my iMac (Retina 5K, 27-inch, Late 2014), running macOS Big Sur 11.6, not boot from external USB drive with an older macOS? I've tried everything without luck. All the external drives show up as eligible options in “System Preferences Startup Disk,” but on startup it keeps reverting to my normal startup disk. Holding down Option at restart does not show me any alternate startup disks. I've tried various external drive bays. Any help would be greatly appreciated.
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Why does my iMac (Retina 5K, 27-inch, Late 2014), running macOS Big Sur 11.6, not boot from external USB drive with an older macOS?
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