fsck.ext4 -p /dev/whatever, right? That seemed to be the answer, but then I read that journaling covers a multitude of sins, and the result from
fsck will just tell you that there isn't a problem with that file system, but won't tell you that you did something dangerous, like shutdown/turning off the system with a file system mounted.
If a log could confirm it, that would be enough. I thought that might be found by looking in
journalctl or grep'ing /var/log/*log, but I was expecting to see strings like "home" or "sda3" to confirm successful unmountings, but nothing came up to indicate that.
I'm running Ubuntu 22.04.3.