TL;DR: My late 2012 Mac mini died (corrupt EFI) upgrading from Mojave to Catalina, I want to use a mid 2011 Mac mini with the hard drives and RAM out of my dead mini. Is this possible?
Drawing on this SO question. It appears that it can. I've also compared the two on EveryMac and it appears possible, except for the OS difference. EDIT: I just read through the specs again, and it appears the memory may be a problem, the 2012 is 1600 MHz minimum, and the 2011 is 1333 MHz, I'll need to look into that further.
My plan is to find a used 2011 Mac Mini server and use it as a host for the two drives (1tb Crucial boot, 1tb Seagate SSHD backup) I have in my dead 2012 plus the 16gb of RAM I have in it. I have multiple backups on the drives, both Carbon Copy Cloner & Time Machine, so I should be able to get to a bootable state. I also have a Win10 VM on Parallels that I'd really like to be able to use again.
For some reason the 2011 servers are about half the price of a used 2012 mini and since I really only need the logic board I don't see why I should pay more than necessary for an older machine, plus with the 2011 mini, I get a faster processor, and an extra monitor.
If this isn't possible, I'm willing to purchase another used late 2012 Mini as a host for the drives & RAM, just don't want to spend more money than I have to to recover the machine.
Best Answer
Your Mac mini 2012 supports OS X 10.8.1 up to the current macOS (10.15.1 at the time of writing). The Mac mini 2011 officially supports OS X 10.7 up to macOS 10.13.6 (High Sierra).
After upgrading your Mac mini 2012 to 10.14 (Mojave) and further trying to upgrade to 10.15 (Catalina), the Mac mini 2011 won't boot with this system disk.
The Catalina installer can be patched to run on some officially unsupported Macs and install the latest system.
The Mac mini 2011 (Macmini5,2) is on this list of (patch-)compatible Macs (with the restriction:
...systems with AMD Radeon HD 6xxx series GPUs will be almost unusable when running Catalina.). The Mac mini 2011 Server (Macmini5,3) - also on the list - doesn't contain an AMD Radeon GPU.I don't recommend to use such patch.