Reset Mac Mini to factory default settings

@BDAqua. Thank you, that's very helpful.

I have not yet erased the Mac Mini hard drive, so I presume that it is important to choose the correct key combination at the start to boot into Recovery mode. The Mac OS Utilities screen allows you to go from Disk Utility (to do the erasing) to Reinstall MacOS, without shutting down between these two stages.

When I get to that point, will it then give me choices of operating system, or does that choice depend on which set of keys I use at the start?

Or, do I shut it down after erasing, and reboot with the right key combination?

As a bit more background info, the old Mini is not at present connected to power or my Display, as I'm using my new Mac Mini. So I'm working from memory - I think that the old machine last had Mojave on it, but I might have upgraded it to Monterey before I bought the new one.

Would your advice be to go for the OS that was on it most recently, or the latest compatible?

Thank you in advance, Ruth N

Ok Thank you. All very helpful. Just hope it goes smoothly.

I've fired it up, it has Monterey on it, and there is a Monterey update waiting. So I think that's the last OS that will work, as otherwise I think it would be offering me Ventura.

I will do the update first before erasing. Seems a bit silly but it might mean it re-installs Monterey with the updates included. I want to make it as saleable as possible.

So thank you again. I will mark your answers accordingly.