The late 2014 Mac Mini (leftover from Belle Pointe) had a dead hard drive. No big deal, right?
Put a new drive in, try to install Monterey and failure ensued.
A Required Firmware Update Could Not Be Installed
popped up. I installed Mojave, updated to Catalina, but no luck. Lots of internet searches later, I found a couple of promising links (all which indicate non-Apple SSD (and I'm using a true HD!)):
an entire discussion about the problem. And a link to a Reddit thread
which actually had the seeds of what to do and how to deal with it.
Other possibilities include using OpenCore to boot it instead of the standard EFI, per Mr Mackintosh on youtube
and on and on.