Reinstalling macOS on a Mac whose recovery partition has an outdated macOS version on it

This is more of an FYI in case it helps someone else, since I wasn't able to find anything directly on this issue and had to sweat a bit to work through it.

The key points are:

1. On a Mac that doesn't have Apple Silicon or a T2 chip plus macOS Monterey (where there is a new System Preferences > Erase All Contents and Settings) you might decide to delete the boot volume if you want to securely erase your (FileVaulted) boot drive.
2. Once you do that you won't have any internal drives that your Mac can boot to, and when you reboot it it will (eventually) show you the Question Mark screen per
3. So then you need to power off, then follow the procedure for booting to macOS Recovery, per
4. Once in macOS Recovery, if you don't have a TimeMachine backup (eg this is an old Mac that has been out of commission for some time), you'll want to "Reinstall macOS {Version Name}".
5. HOWEVER, if this Mac shipped with an older macOS version, like Sierra, that is no longer being signed by Apple, then when the Reinstall process goes via the internet to Apple to download macOS, you will have no choice about which version is tries to download, and it will fail to download that older version, giving the error message "The installer information on the recovery server is damaged". Unhelpful message, but that's what it means.
6. At that point you have no choice but to download a later, supported version of macOS and create a bootable USB drive with that.
7. To do that you need another Mac, and that Mac needs to be compatible with a version of macOS that is also compatible with the older Mac you are trying to recover. That other Mac can be either Intel of Apple Silicon however (thank goodness).
8. The download links can be found here , and (at least on Monterey) those will all always cause App Store to open, but you will be given the option download rather than install that version.
9. If you are downloading the same version (ie major version) of macOS as you have installed on this Mac, this Mac must be fully updated before you try to use the downloaded installer. If you are not fully updated you will see an error when you try to run 'createinstallmedia' below. That error message will be "/Applications/Install\/Applications/Install macOS Monterey.app does not appear to be a valid OS installer application". Also a traditionally opaque message. So upgrade this downloading system first. I don't think you would see this issue if downloading some earlier version of macOS. I'll just note, with rare thanks to Apple, that in Monterey a download will resume if it gets interrupted and you later initiate the download again. On the other hand, the download server is very slow, and it takes about an hour to get a 12GB download completed, so fewer thanks to Apple on that one.
10. You then need to follow the steps at to format a USB drive (16GB is required I think), make it bootable, and copy the installer to it via 'createinstallmedia', as above. Note that this is likely to take dozens of minutes to complete so you'll need to be patient here. And, again, not the possible error message as above if what you downloaded is later than what you currently have installed on this Mac.
11. Once that process completes, eject that USB drive (ie use Eject on the drive in macOS) and connect it to the Mac you need to recover. Power-off that Mac, then power it on again with the USB drive connected. Since you don't have an internal bootable drive the Mac will find the bootable USB drive. If for some reason you do still have a bootable internal drive you will need to hold down the Option (Alt) key immediately after power-on and select the bootable USB drive as the boot target (ie as the drive you want to boot). You will also need to connect to the internet, typically by selecting a Wi-Fi SSID and entering the key. If you see a spinner beside the entered key for an uncommonly long time, that means you need to click the "-->" arrow beside the key (hitting the enter key doesn't seem to always do it).

At that point you are hopefully into the process of installing macOS onto an automatically-created new internal boot volume, and that's where this story hopefully ends. Lots of micro-frustrations and -learnings in there that I would love to save someone else from. I do think Apple could do a better job spelling out some key points in this - particularly what these error messages mean.

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