I can't open an autorun.inf file on my Mac mini, what should I do?

as stated autorun.inf is just a text file you should be able to open with just about any text editor

https://en.wikipedia.org/wiki/Autorun.inf

A simple example

[autorun]

open=setup.exe

icon=setup.exe,0

label=My install CD

if open= an exe file then it's a windows program which will not be able to run on your mac without a virtual machine, bootcamp or some winebottler or otherwise emulator

if it points to a pdf in on the cd you can just manually open that file

If you installed Windows either via Apple's Boot Camp feature or by setting up Windows in a virtual machine then yes that copy of Windows would indeed run this just like a real Windows PC.

This is a file extension used to run windows program and it won't work on your Mac.

An autorun.inf file as mentioned by miyalung is a special file used to trigger the automatic running of a program in Windows. This would happen when you inserted a disc containing that autorun.inf and matching program.

It originally was used on floppy disks to install programs but later when floppy disks became obsolete still used on CDs and DVDs containing software.

It was often used to automate running an installer to infect a Windows PC as well.

Macs have in the past had their own method of defining something to autorun when a disc is inserted but this feature was removed decades ago mainly again due to the risk of this being hijacked to automate infecting a computer. See - https://www.macdisk.com/cdstarten.php

The fact your 'auto service and repair manual' - presumably on a CD or DVD disk has an autorun.inf which as discussed is purely for the benefit of Windows does not necessarily mean it could not be used on a Mac. You would however have to find if there is one a different method of 'opening' the contents.

Some CDs and DVDs of this type may contain just HTML files so you might find a master something.html file which will let you navigate the rest.

Without knowing the names of what else is one it we would not be able to be more definite. Perhaps a screen capture showing the contents would help.