Well, I think I won’t even try to do an update for at least 24 hours or more. Live and learn 
I reviewed the repos, checked my mirrorlist file, ran pacman-mirrors --fasttrack and checked my mirrorlist against the web page again. I used pacman -Syu and tried pacman -Syyu and the same results. I’m on a VM and restored for each attempt.
The last two errors have been "error: could not extract .... (Zstd decompression failed: Corrupted block detected), as mentioned here. It has been different files. I think the repos are still syncing (United_States), even though there is a checkmark indicating “Up to date”.