I rebooted to move the server to a new location, and after restarting, this problem went away. I never trust when problems just disappear like that. :(

Thanks, @JaromandaX. I added the alias when it wasn't working without it. I've now removed it again. No operational change.

I have incorporated every "answer" here (on raspbian bookworm system) without success. Script is self-explanatory. In spite of the redundant "answers" here, yet the $HOME/.config/chromium folder is included. Have tried each solution to no avail. NOTE: backslashes removed by SO. Replaced here with + for visibility: cd /; zip --symlinks --recurse-paths --quiet ~/zipfile.zip $HOME/.config -x $HOME/.config/chromium/**+* "$HOME/.config/chromium/*" $HOME/.config/chromium** $HOME/.config/chromium+* $HOME/.config/chromium/+* $HOME/.config/chromium/**/* 2>&1; cd; unzip -l zipfile.zip |grep chromium

Thank you for that information, @GregAskew. So are you suggesting this means that later versions, since they are uncertified? I will try one more time with 14.04 (it's been a long time) but I believe I get the same result there. Not sure what you're trying to say.

Thanks, @JourneymanGeek Not dumb; I'd actually forgotten about that. But there is nothing in that slot in either of these systems.

@symcbean I will update my question, but here's the gist: Even if I remove/unplug all other devices, leaving only a USB distro and a USB target, this is the end result. So, no to all the above.

Thank you, @RomeoNinov. Can it be moved? Or shall I ask it anew?

@RomeoNinov I think it's obvious I expected a response similar to this, so thank you for addressing the first half of that. But in order to move forward, do you have a suggestion where this question might be appropriate? Or do you feel it's enough to tell a person what he should not do when he clearly suspects that to be the case?

@symcbean what would you like me to say about the configuration of storage when, for example, the only devices in some configuration attempts include only a USB disto image and a USB target?

@Tomek - thanks for your replies. Yes, you were right on two counts about the public key. Recreating the public key rom the private made that error go away; and the error was also issued by the port 22 service. Please see my most recent update of the question. I'm lost.