It seems that the signing key is not built in and can’t be added so for most distros you have to disable secure boot. Also had to change from RAID to AHCI for the NVMe to be recognized. Once I got it installed it works very well. So well that I nuked the Windows partition. 
I want to set up my G5 5000 desktop to dual boot Linux and Windows. It sees the usb drive at the bios level, but refuses to boot from it. Selecting it manually at startup results in the diagnostic routine.  I’m confident that the drive has been properly created and that the iso is good. Any other ideas?
Can’t boot from Linux USB drive