I have been trying for 4 days to do a full kali OS install on a usb drive (not a live usb, FULL). I can not find anyone facing a similar situation anywhere I look. I have created a live usb (via dd) to do the install and the live usb works perfectly fine on the Mac. Once I install kali onto the desired usb, however, the Mac bootloader refuses to recognize it or even show it as an option to boot from. Any suggestions or similar situations?

Kali version: 2018.4 amd64
Mac info: iMac (Late 2013), OS X Mojave