unable to boot to any menu, only os

trinkey wrote:

On my late 2012 Mac Mini, I installed Ubuntu Linux as the one and only OS on the computer. However, now, I am unable to boot into the recovery menu, boot selection menu, etc., as they all just result in no output going to my monitor.

Have you attempted Internet Recovery? See Use macOS Recovery on an Intel-based Mac - Apple Support It's at least worth a try, although whatever you did to install Ubuntu exclusively may have nuked both Recovery & Internet Recovery.

If that doesn't work, you probably need a bootable macOS installer flash drive in order to reformat the Mini's system drive and install macOS. I doubt you can create that under Ubuntu, you probably need another Mac in order to make a bootable installer drive. See these articles for the procedure:

• How to download and install macOS - Apple Support
• Create a bootable installer for macOS - Apple Support

You will need to reformat your system drive as APFS. And you should be able to install Catalina (10.15.x) on a late 2012 Mini. Note also that 32-bit apps will not run under Catalina or later versions of macOS.

AFAIK, to boot from the bootable installer flash drive, you should only need to hold down the Option key when starting your Mac. Read the "Use the Bootable Installer - Any Other Mac" section of Create a bootable installer for macOS - Apple Support

Can you Option Boot the Mini by holding down the Option key immediately after the startup chime? Make sure to use a wired USB keyboard since a wireless keyboard may not go ready quickly enough. If you can get the Apple boot picker menu, then try using Command + Option + R while still sitting on the Apple boot picker menu assuming that macOS 10.12.4+ was installed on this Mac at some point in the past. I know this works on the later Intel Macs, not sure about a 2012, otherwise just use those keys immediately after the startup chime using a USB connected keyboard.

Also, make sure you have the Mini connected directly to the router using an Ethernet cable to bypass any difficult to troubleshoot WiFi issues.

Can you still boot into Ubuntu? And is Ubuntu working Ok? If you are having issues with Ubuntu, then maybe the same issue is why you are having trouble booting into any other modes.

Try booting into the Apple Diagnostics. If you see an error message something like "Cannot Load EFI/Drivers/TestSupport.efi", then it just means your Mac is one of the ones where Apple messed up the system firmware causing a compatibility issue with the bootloader for the Apple Diagnostics and does not tell us anything useful.

Try an SMC Reset and a PRAM Reset (hold the PRAM Reset for at least three chimes).

Are you using a Wired USB Mouse, you should be.