Can’t Delete Original Admin User on macOS High Sierra

I recently migrated to a new MacBook Pro. The old one was on High Sierra, but the new one wasn’t. So I created a temp “admin” account to do the upgrade, then do the migration with Migration Assistant.

All seemed okay, but when I went to delete the original user account, I couldn’t. And I don’t mean “you don’t know how to delete accounts” couldn’t. I mean, I tried every possible way, and it wouldn’t couldn’t.

I found this thread on the Apple forums with people having the same problem. After trying everything else…