Chosen Solution
I bought a Crucial 1 TB SSD and plugged it into my Thunderbolt 3 port. And when plugged in, my mac (2018 Mac Mini with upto date OS) it just won’t start. With verbose mode, no text appears on screen: just the apple logo. Note: macOS boots from the internal SSD, this external SSD is just a plain storage unit. What I’ve tried : Some have speculated it could be related to the eGPU, but unplugging the eGPU doesn’t solve anything.I tried removing the T2 security “Boot from SSD” - no changeI’ve checked the boot order, it’s set to the internal SDDI have 3 HDD on the USB ports that work just fine So far, the only solution is to unplug the SDD, and plug it back (which is not really a solution, is it ?)
There are a couple of issues trying to boot from an external drive besides the systems T2 security controls. First the drive needs to be formatted with GUID and the drive needs to be setup with APFS not HFS+ as macOS Mojave and newer requires it. The next is the version of macOS needs to be what the system requires so you do need to make sure its setup with macOS Mojave or newer. When you start your system you do need to enable the Startup Manager to select the drive you want to boot up pressing the Option (⌥) key. Reference: Mac startup key combinations
