Aw, fsck!
Although everything installed okay, as I said up above, not all is working okay now. Friday night I hibernated my laptop, as usual, and Saturday morning it appeared to restore normally - all workspaces, all apps just th way I left them the night before, etc. Then I got the message that there's "no Internet."
Indeed, I wasn't connected, and couldn't connect until I shut down and restarted the laptop. I thought it might be a one-time glitch, or I'd done something wrong myself, and since everything was now working well, I went on with my Saturday chores, and forgot all about it.
Saturday night, as usual, I again hibernated the laptop, and Sunday morning it again appeared to restore everything correctly -- until I tried to access the network. Once more, there was "no Internet" and I now realized it wasn't a one-time glitch. I rebooted, but that didn't resolve anything. So I shut down the laptop and restarted it, after which everything worked properly again. This had never happened before this most recent update.
I don't know whether this is a Solus issue, or a KDE issue. I'd be interested to hear from anyone else who has had the same problem, especially if you're running a different DE than Plasma.