For ages, I’ve had an issue with my Mac mini where it wouldn’t shut down properly after some unknown “event” occurs. Either it was running for a certain period of time, I connected to some network share or something else. Whatever it was I could never figure out the exact cause.
What felt like every month or so I’d do a search to see if any body had figured out the issue yet and recently I found this https://apple.stackexchange.com/a/412649. Incredibly the outlined solution seems to have solved the shut down issues I was having. As it turns out, a few years ago I had implemented a “fix” for slow cli apps that was caused by the code signing subsystem of macOS. This fix, in newer releases, caused some kind of issue that prevented the system from shutting down properly. By removing terminal as described my Mac mini has been able to reboot and shut down without issue.
In the post is a link to this site explaining the issue a bit more deeply – https://sigpipe.macromates.com/2020/macos-catalina-slow-by-design/.