User Profile

Talked to an Apple guy today who was more knowable in this area and related things. He was able to shed some light on the different things going on here. Some is T2 related, some perhaps beta related, and some software related, and some documentation related.It seems that a Mac system generally cannot boot a version of macOS earlier than the version that originally came installed. So a Mac that came with macOS 10.14…generally cannot boot versions 10.13 or earlier. My 2018 Mini came with 10.14 Mojave…so any boot attempts at Mavericks, Josemite, High Sierra, etc wont work. What seems very odd is that if you have earlier versions (I had 3), they will show in the Mojave Startup Disk selection area, will allow you to select them, will attempt to boot…and then fail with various error messages that are less than informative. It seems the system should know its limitations, either not show these options, or prompt with a message indicating the lack of any expected success. Seems some room for improvement.The T2 based macs have a security boot utility that allows you to set external boot options. It has 3 levels of security…High, Medium, and none. If you read the docs on the None selection, there is nothing there to indicate that there might be other restrictions (like above) that would prevent boot. Clearly there are. There is room for improvement here in the documentation.I had two of the 2018 Mini units. The first died about after 10 days. Before it went south I had successfully installed and run the first betas of Catalina. When the second 2018 unit arrived the SSD drive from the first with Catalina would also not boot. No clue of why. The Apple guessed it was beta related. The only way to get around that was to erase the disk and reinstall Catalina. That worked.

Same issue here. No clue on how to fix.