I asked here several months ago whether the Ubuntu upgrade process had been improved from "better off doing clean install" as it was when I came up from 14.04 to 16.04 (and from 16.04 to 20.04) and was told I shouldn't worry about it; upgrade problems are rare.
For the past week, then, I've been getting a recurring popup message nagging me to upgrade, reminding me that Kubuntu doesn't have 5 year support, but instead Kubuntu 20.04 will lose support in April of 2023 -- and offering a "one click" upgrade start.
This afternoon, with a few hours when I had nothing pressing to do, I started that upgrade. I was first given the message that "third party repositories are being disabled" which I've also been told, here, isn't a red flag -- I just have to re-enable those repositories after the upgrade is complete. Then downloading began, and completed in under 25 minutes, followed by applying changes, which was forecast to take about an hour and a half.
I left to make dinner, and came back to a message that Python3 had failed to install and my upgrade would continue, but the system might not be in a usable state afterward. Minutes later, another message announced an abort of the upgrade -- it gave a systemd command that I thought was telling me what it was going to automatically do, along with a reboot nag and a crashed program notification (which didn't say what had crashed).
Then I was returned to my regular Kubuntu desktop. I clicked the reboot prompt, and got a normal-looking shutdown.
Then the computer didn't power back up automatically as it usually does after a restart command; it hasn't done so since then on either a CTL-ALT-DEL from GRUB menu or reset button. Both result in a power down and require pushing the power button to start up again.
I get the GRUB menu I'm used to finding, so I ran a Google search on my laptop (still on MATE 16.04, but at least it runs), and found this blog article that told me to start by booting to recovery mode. Which I tried, but the recovery mode menu screen I get is very broken, with a lot of broken formatting leading to a final message set saying I'm in "emergency mode" and offering a number of systemctl commands -- none of which will run if I type them; nor do I get a login prompt if I try a normal boot and get to emergency mode without the recovery mode menu.
Help! This is my primary daily driver system; I can't do anything productive or creative without it. I have no other operable operating systems on the desktop machine.
Hardware details (if it matters): AMD Fx8350, 32 GB RAM, GTx1650 w 4 GB VRAM, startup drive is a 256 GB SSD with what I believe was enough free space in the system volume.
Update 12/12
I found this question with the exact (I think) "emergency mode" message and I hope to try the methods given in that answer to get out of emergency mode to a useful command prompt.
