Confirm Before Shutdown
How this Rule works
When the shortcut is pressed, Show Confirmation displays a dialog. If it is cancelled, the Rule stops; otherwise Shut Down Computer runs. There is no Condition.
Configure and try it
Choose an unused shortcut and change the dialog to clearly say it will shut down the Mac. Enable the Rule, press the shortcut, and test Cancel first. Save your work before testing confirmation.
Requirements and limits
Show Confirmation requires Rulr Pro; the shortcut requires Accessibility. Confirming requests a real shutdown, and open apps or unsaved documents may affect the shutdown process.