Ah! I found a nice button script from Juan Diego Tórtul in the HA community forumIn the automation editor you will find the action you require under “home assistant supervisor” in the “other” category.
type: button
tap_action:
action: call-service
confirmation:
text: confirm HA shutdown
service: hassio.host_shutdown
service_data: {}
target: {}
show_state: false
show_icon: true
name: Apagar sistema
icon: mdi:power
hold_action:
action: none
icon_height: 30px