I actually started a new download of a Manjaro live image (since I’ve had dozens of kernel updates, and probably many btrfs-tools updates since the one I had on a flash drive sitting around for who knows how long). And I had to head out of the house for a while anyway.
When I got back, mounting the root subvolume worked, and fixed grub! So I didn’t even need to boot the image I downloaded.
One problem, it undid the whole reason I needed to restore a previous snapshot. An update broke my networking to all of my VMs, and I needed them to do my work. So I had to restore to undo the update, then worry about troubleshooting the problem with the update later.
grep 'upgraded.*linux515' pacman.log | tail -5
[2022-09-13T02:48:09-0600] [ALPM] upgraded linux515 (5.15.60-1 -> 5.15.65-1)
[2022-10-06T20:13:03-0600] [ALPM] upgraded linux515 (5.15.65-1 -> 5.15.71-1)
[2022-10-10T21:22:02-0600] [ALPM] upgraded linux515 (5.15.71-1 -> 5.15.72-1)
[2022-10-15T23:44:32-0600] [ALPM] upgraded linux515 (5.15.72-1 -> 5.15.74-3)
[2022-10-18T16:59:21-0600] [ALPM] upgraded linux515 (5.15.72-1 -> 5.15.74-3)
I restored the image back to the 2022-10-15 snapshot because I think the kernel upgrade to 5.15.74-3 (which was only part of that update) on 2022-10-18 caused my initial issue. This is what made me restore in the first place. I’m only guessing at that, I just needed a quick way to undo that update, so I used the Timeshift restore feature. (But at least I was able to get my work done, while working on the older RW 2022-10-15 snapshot. Since the VMs I work in, aren’t affected by these snapshots.)
So basically I’m back to square one. Grub is fixed, but I am running the snapshot which made me need to restore in the first place.
I least I can try to downgrade the packages that were upgraded from here I guess? And I did learn a lot thanks to you @Zesko. I really appreciate it.
I am still really confused why Timeshift operates this way. By using the restore feature, I was temporarily able to work on the snapshot I wanted to. But I had to undo the entire restore to fix how it did the restore.
I am dead tired, and going delirious. I need to get some sleep and come back to this fresh. But thank you so much for all your help @Zesko.