How do I restore the original or a compatible version of mac-os on my 2012 mac mini

Are you using recovery mode (start device holding down command + R)? A 2012 i5 or i7 max mini can run MacOS Mojave so there is no version of MacOS too new for a 2012 intel Mac mini. The 2011 models cannot run MacOS beyond 10.13 though.

If you're getting SMART disk errors then there well may be something wrong with your hard drive that is causing the install to fail.

jc_x_c wrote:

..The problem I have is all the install option fail because they say the disk has 'smart' error...

SMART error means you have a failing drive which is what any installer

checks first regardless of whether the OS can actually be installed.

The information is collected directly from the drive via firmware.

Just to add, SMART has been supported by all ATA

(SATA and PATA) since their existence.

"..Not so sure about SMART errors I think the error is more

that the disk doesn't have the hardware to report SMART.."

The fact that it is reported at all means it exists. I know it is not

the answer you really want to hear, but the HDD is failing.

It happens, and probably has been going downhill for some

time.

If macOS is telling you the drive has SMART errors, then you have a failing hard drive. Your best bet to securing the drive is to enable FileVault if you haven't erased the drive yet. If you have erased the hard drive and you were not using FileVault, then your best option is to try Secure Erasing the drive using Parted Magic. You can create a bootable Parted Magic USB drive using Etcher and the free version of Parted Magic available from the majorgeeks's download link here.

Option boot the bootable Parted Magic USB drive and select the orange icon labeled "EFI". Once you reach the desktop, there should be an icon for erasing the drive. It will provide you at least two options. Select the "ATA Secure Erase" option if possible. This will use the drive's internal firmware to write zeroes to the drive and will take at least several hours to complete depending on the size of the drive and how bad it is failing.

It should have. As I say, a 2012 Mac Mini is compatible with the current MacOS 10.14. Every Mac sold in the last ~15 years has had SMART capable hard drives all the way back to the ATA bus drives.