I have a boot hard drive from an old Mac and a new Mac. I want to boot the new Mac from the old Mac's boot disk (preferably without having to take the new Mac appart) So I attach it via USB, configure it to be the boot drive in System Preference and reboot. Almost immediately after the chime, the new Mac displays the grey prohibition sign 🚫.
The new mac is running 10.14. The old Mac that I'm trying to boot into is on 10.13.
Any ideas as to the cause of this? How about ways to troubleshoot?
According to the internet, booting from external drive is possible these days. And the prohibition sign appears when a bootable drive is found. So I don't know what's the problem.