My MacBook Pro 13" Mid-2012 running OSX 10.11.6 is not displaying externally connected disks in Startup Manager. I have a brand new Crucial SSD cloned from a different machine, that I would like to boot from. I know the SSD is fine as i've tested it externally with another almost identical MacBook pro (except running OSX 10.14.3) and have no problems getting it to boot. I also know the USB ports on the machine are fine, as once logged in I can see other USB devices and hard drives in Finder, but NOT the Crucial SSD (although it is visible in Disk Utility). However, I can't see these other USB devices and hard drives in Startup Manager. The Crucial SSD doesn't work when trying to boot it internally either. I have tried resetting the NVRAM and SMC. Below are screenshots from Disk Utility on the original MacBook (OSX 10.11.6), and then then working MacBook (OSX 10.14.3). Is it perhaps something to do with how the Crucial SSD is formatted?