At the Database Upgrade Required step, the update process reports an error and invites to revisit the page until no errors are reported. After clicking the Details link, I get this:

I don't think the intention was to get that display. I imagine it was meant to be some rich formatting with line breaks, bold text, code sections, etc. The comment markers around Please delete these directories to prevent errors. might be the culprit. I'm saying that because I have ssh'ed into the server and have checked all permissions as well as ownership of the directories and files, which are as they've always been for years now.

EDIT: And of course, I can no longer view the dashboard, as I'm brought back to that very page with the very same Details link. I was using the habitual automatic update.