I've dealt with this in the past two weeks, actually.

I had an M1 MBP that I needed to re-pave with Monterey. Yes, it's end-of-support, but it's also only 4 years old. And should run on that Mac.

So, first step, I make a USB installer, and run it. Great. Reboots, and says "FYI, this is an unsupported OS. You can install a newer OS instead, or run Monterey in "Reduced Security" mode." That was fine for me.

"Installation of Reduced Security mode failed." Nothing else. Eventually my understanding of this was because the machine had been upgraded previously all the way to Tahoe, that somewhere along the line some firmware or something in the EFI had been upgraded and was too new for Monterey.

So what then?

Hmm, more research. "Do an IPSW image restore via DFU", i.e. pave it with a largely installed image. Could work, might have the same issue, but I'm stuck right now, with a Mac I can't install anything on, a four year old $3,000 brick.

Alright, I have a Mac Studio. I get the IPSW image, and Apple Configurator. Connect the two as per Apple's instructions, and (different here to OP), the MBP does indeed show up in Configurator as being "not booted, DFU mode".

Apple's instructions, "Drag the IPSW image onto the DFU 'box' for the target Mac". No. It doesn't light up like it's accepting a drag and drop, and indeed it doesn't. Nor does it accept a "restore..." or similar from the Configurator menu options. There's nothing in Configurator that seems to allow you to image the MBP.

Off to ChatGPT, Reddit, etc., I go.

Much repeating of the same. However, ChatGPT pokes a little button. Near the very end of its answer, it says "Newer versions of macOS may have limitations on the age of the image they might restore. You may need a slightly older macOS to do this. Even an Intel MBP running Ventura could work."

As fortune has it, my fiance happens to still have her old i5 MBP with touchbar, and the latest version of Ventura...

Alright, I need Configurator on this laptop.

No, says the App Store, "You need macOS Sequoia to install Configurator".

I find someone who has helpfully zipped up an older version of Configurator that runs on Ventura, and in the end, it works.

But Apple's docs absolutely are incorrect/incomplete about Configurator, and DFU restores.

"You can use Restore... in the Configurator menu to select the software image". No, you can't, even leaving aside the "old/unsupported". It actually means restoring from a "backup" (presumably Time Machine, though it doesn't specify) and you can't select any file or image.

"Drag the image onto DFU". Doesn't work in that situation, no error, no "hey, you're doing the right thing but I can't do this", just acting like a fool trying to drag the image onto DFU only to have it bounce off.

Like I said, I didn't have the DFU port issues, but Apple's docs on how to make this happen were either non-existent, or incorrect about the process, or flat out told me I couldn't do it. But mostly non-existent and overly simplistic covering the most basic scenarios only - which I get for general support, but by the time you are "connect to a second mac in DFU mode and run Configurator" in their own words, we're way beyond simplistic "you can just install a newer macos" type "instructions".

No, it's not easy. I just said, in the comment you replied to, "I'm not even sure that I have all the prerequisites on hand."

> I have personally tested this

On my Mac model?

To be clear, I'm saying that the doc is wrong about my specific, relatively new Mac model, which I bought a year ago. I'm not claiming that the doc is wrong about other, older Mac models.