UPDATE: I tried once more to disconnect the internal keyboard and connecting a USB keyboard and the scrolling issue seemed to go away - and I was able to OPTION-Boot and boot to diagnostic mode with the USB keyboard. So I did some more digging - actual digging. I dug the down arrow cursor key out and it looked like there was chunk of lint in it. With the key taken apart the machine DID NOT have the issue. I cleaned the key and put it back together and it started scrolling again. I took it apart again and cleaned it better and now I think it works. If it continues to give problems I think I will need to replace the keyboard (top case assembly). Sorry for not recognizing this earlier and thanks for the responses.

@danj I disconnected the headphone flex and now the built-in speakers are enabled again. So, my theory is that there has been a mechanical (or electrical) failure of the circuit that detects when headphones are inserted. In this case, the machine thinks there are always headphones inserted and (correctly) disables the built in speakers.

Adding SSD Drive to PCIe model appears to have the answer. I also found this fairly detailed explanation of exactly what I was trying to accomplish https://ghouletech.co.uk/upgrading-non-ssd-late-2014-mac-mini-fusion-drive/

I found this on Medium.com posted by Robert Hammen: Similar to how iOS is configured, macOS is now on a separate partition from user data, which acts as if it is read-only (but in beta 1, it’s merely SIP-protected). In the beta, you’ll see “Macintosh HD” and “Macintosh HD — Data”. Data is a separate volume mounted in /System/Volumes. OS-installed applications live in /System/Applications, but the Finder presents them in /Applications as well. Apple calls the technology “firmlinking”. Beta 2 will be fully read-only by default. Maybe this will help someone to update the commands required to remove a user folder and remove the .AppleSetupDone file (or whatever needs to be done to trigger the OOBE or new computer setup at startup. Update (02/26/2023): Just to update this thread - I've been doing the following commands for machines I'm going to sell: Big Sur/Monterey (From Recovery Terminal, not Single User) csrutil disable rm /Volumes/Macintosh\ HD/var/db/.AppleSetupDone rm /Volumes/Macintosh\...

Has anyone (besides OWC) reverse engineered the sensors required to make the 2009-2012 iMacs work with 3rd party hard drives? The OWC in-line digital thermal sensor products work great but they cost almost as much as a 120 - 240 GB SSD that are affordable to keep these old machines going. If someone could make and sell these for half their cost or less I think there would be a lot more people keeping these old iMacs going. They’re still useful.