(Recently) Working internal hard drive being reported as unformatted after external drive boot

Disk recognition problem identified: it’s that high Sierra reformatted my internal SSD drive to apfs file system when I upgraded from Sierra, which isn’t recognized by the older Sierra OS on my portable drives. There’s some fix by Paragon called a retrofit kit which I have to explore. I’m kind of surprised when I searched for this I didn’t find anything; obviously I did the wrong search, but im still not sure what grading would’ve gotten a hit.

As a follow-up, I unplugged the charger and let the battery run down. For some reason this generates a restart when the charger is plugged back in. It booted right up to the internal drive. So obviously the drive is working. I then ran a diagnostic with disk utility, no issues. I’m pretty stumped as to what the problem is. A local computer shop had opened it up the other day because it had gotten stuck on the grey—black?— screen with cursor arrow for a different reason last week (a series of stupid things I did) and they cleaned it up a little but I can’t see how that would lead to the HD being reported as unformatted when booted externally. Wondering if Inshould re-post under Mac OS or elsewhere.

I know it’s been a minute! I used to post as ptrash, never got many responses and always blamed it on my forum moniker (?). There was a DIY site some dude ran, I can’t remember it’s name, this was in the early PPC days, when accelerators were big. I think you were on that one too.

So I’m not techie. I had to look up SMC. Could that explain the issue with the internal HD disappearing when booted to external system? Unfortunately we tried using a system on a usb stick at my local computer shop and it wouldn’t complete the start-up, so I can’t say if this issue is limited to this portable drive (which worked fine booting up in the past, even post spill, which was maybe 2-3 yrs ago). I can tell you we again unplugged the battery and restarted to the internal drive fine, then tried booting off the portable G tech drive again with same outcome—hard drive reporting as unformatted . (I realize the only way to isolate the issue is to try and boot from another external source, I’m going to have to find one somewhere on something better than usb stick)

I found another bootable external drive, a different model G tech. Same results, upon booting to external (Sierra OS, same as other one) drive internal hard drive is reported by disk utility as unformatted, and is not a start up option in system preferences

re not specifying initially Sierra being the OS on the external drives, I know, my bad, I didn’t want to overwhelm people with too much info.