

Running poweroff
is one of the correct ways on anything Systemd (details). If that doesn’t work then something is broken.
If you haven’t done so already try looking into the journal. sudo journalctl -b -1 -e
will take you to the end of the log for the last boot.
To be fair showing the overview on startup makes perfect sense on vanilla gnome, it’s only dumb if you install one of the two specific extensions that partly replace it.