i3wm shutdown config - https://faq.i3wm.org/question/239/how-do-i-suspendlockscreen-and-logout.1.html

i3exit.sh

#!/bin/sh
lock() {
    i3lock
}

case "$1" in
    lock)
        lock
        ;;
    logout)
        i3-msg exit
        ;;
    suspend)
        lock && systemctl suspend
        ;;
    hibernate)
        lock && systemctl hibernate
        ;;
    reboot)
        systemctl reboot
        ;;
    shutdown)
        systemctl poweroff
        ;;
    *)
        echo "Usage: $0 {lock|logout|suspend|hibernate|reboot|shutdown}"
        exit 2
esac

exit 0

i3wm config

set $mode_system System (l) lock, (e) logout, (s) suspend, (h) hibernate, (r) reboot, (Shift+s) shutdown
mode "$mode_system" {
    bindsym l exec --no-startup-id i3exit lock, mode "default"
    bindsym e exec --no-startup-id i3exit logout, mode "default"
    bindsym s exec --no-startup-id i3exit suspend, mode "default"
    bindsym h exec --no-startup-id i3exit hibernate, mode "default"
    bindsym r exec --no-startup-id i3exit reboot, mode "default"
    bindsym Shift+s exec --no-startup-id i3exit shutdown, mode "default"

    # back to normal: Enter or Escape
    bindsym Return mode "default"
    bindsym Escape mode "default"
}
bindsym $mod+Pause mode "$mode_system"