Recently moved from a 2012 Mini to a 2018 Mini. The existing 2012 system has 6 bootable partitions, 5 of which were external USB based drives/partitions. I needed all the external drivers to work on the 2018 system, which has the T2 security chip.
The core OS on the 2018 model (10.14.5) worked fine. None of the external drive partitions would boot. This ws the default case. It was also the case after the Secure Boot Utility was used to set No security and allow external boot drives. All resulted in various errors about the need for software/drive updates.
I had a couple of different ciscussions with various Apple folks via support chat. The info there is varied and not consisent at all. It seems clear that few have dealt with T2 issues so far.
I have one external drive that now boots, but involved some changes. I did an disk image copy on the 2012 system, then moved the drive to the 2018, erased it completely, and then did a image restore. It then booted. IT has APFS before the image save and HFS+ affter.
It seems like the image restore actions from the 2018 system put a signature on the drive/partition that perhaps the T2 system recognizes and allows boot. I dont see any docs on this at all, and this seems inconsistent with the concept of "No Security" selected option from the Secure Boot Utility.
Any one else see this issue or have any thoughts on whats going on?
After more days of continued grief with this mac, today it just totally died. Hiting the boot button yields no sound and no display at all.
It does back to Apple tomorrow.