RHEL8 SSD no longer boots

Hi All,

I somehow caused my internal NVMe SSD drive that contained my RHEL8 system to no longer boot. This occurred while I was installing RHEL9 on a new internal NVMe SSD drive, which I installed after removing the existing drive containing my RHEL8 system.

Once the RHEL9 system was up and running, I put the RHEL8 drive into an external USB enclosure and plugged it in so I could copy my files from that drive onto the new RHEL9 system. For complete details, see https://access.redhat.com/discussions/7053483.

Rather than copying my files from the old drive onto the new one, what I now need is to get the RHEL8 drive to boot again so that I can get back to work and deal with the RHEL9 system setup and file copying later. I'd forgotten how much effort it is to get a new OS to the point where it's usable, so now I just need to get back to work using the RHEL8 system again.

I've dealt with BIOS settings numerous times over the past 15 years or so, each time as a result of upgrading to a new OS (three or so Fedoras, a couple of CentOSs, and most recently RedHat 8), so I don't think the BIOS settings are the problem (although, of course, I could be wrong). It's my belief that something happened to the RHEL8 drive when I accessed it as a USB drive that has made it unbootable, which is something I've heard can happen (and I believe have experienced myself).

Can anyone please help? My understanding of boot drive configuration, or any drive configuration for that matter, is extremely limited so I'm very much out of my depth here.

Thanks, mitch