I learned a lot from today's adventure but it didn't have a very happy ending.
Since I had the NVMe drive in its enclosure already, and wasn't using it for anything else, I thought I'd install Solus on it while I was waiting for my new flash drive to arrive tomorrow. That turned out to be a worse idea than I'd thought.
After selecting the installer from the F12 boot listing, I started the installation process. When I selected the target to be installed, it was suggesting a 256GB drive, and I was pretty sure that must be the NVMe drive, because I was had thought that the SSD in this laptop was 500GB. That was a mistake.
I finished the installation and rebooted, and was not surprised to see a new installation with nothing configured yet. That's what I expected to see. But after configuring what I thought was the NVMe drive, I wasn't able to boot the laptop without the NVMe plugged in. That's when my general comfort level changed quite a bit.
Long story short, you know by now what happened. I've installed Plasma on so many computers here that it was pretty quick and easy to install it once again. And likewise, I've configured Vivaldi so many times, and I was able to sync that easily. I have a copy of collected addresses saved on my NAS, so Thunderbird was easy. And likewise, my bashrcAdditions and fstab additions are stored there, so those were easy to implement as before.
But what I DIDN'T find easy to do was to get Bluetooth working again. It's part of the Wi-Fi system, and the Wi-Fi is working fine. But Bluetooth, which should be controlled by the same switch, does not come on. I don't know why the software mishap I suffered today should have nuked my Bluetooth, but something did.
I'll order another Wi-Fi radio from Amazon for delivery tomorrow, and hope that installing it (a trivial task) will restore Bluetooth. The BIOS is set to activate both Wi-Fi and Bluetooth with the Wi-Fi switch, but turning it off and them back on controls just the Wi-Fi now.
The reason Bluetooth is so important to me is because I usually use one BT mouse and one BT keyboard to work at this laptop, control the media computer for the TV and occasionally text with my phone. (I'm no good at two-thumbs typing, but with the mouse and keyboard connected to the phone, I can text like a teenage girl!)
If you don't hear a lot from me in the near future, know that I'm workin' on it.