Install raspberry pi tools from repo. Pi3B+ shutdowns, if Kodi power off is used in libreelec 10. You would have to remove power after that to get it reboot. Click link does talk about adding missing button to Pi.
"with most computers that is a no-no."
Modern operating systems have features in place to handle abrupt power loss. power off is not recommended, but options for doing it are there and in some cases it is the only recovery option that you have. With libreelec it is even easier cause OS is on readonly file system. Your biggest power off problem would be with attached NTFS storage devices.