Primary and Secondary Lights

@123 You are right the selector should be an entity selector not a target selector.

The name of the blueprint should not be synchronize. Its probably misleading.

The purpose of this automation is to have a primary and a secondary lights in the same room when it doesn’t make sense to have only the secondary light on. Like in the bathroom with the main light (celling) and the mirror light. When you turn on the mirror light the automation turns on the main light. When you turn off the main light the automation turns off the mirror light. Just this.

Like this is working fine for me

blueprint:
  name: Synchronize Primary and Secondary Lights
  description: Turn on the primary light when the secondary is turned on and turn off the secondary light when the primary is turned off.
  domain: automation
  input:
    primary_light:
      name: Main light
      description: This is the primary light, will be turned on when the secondary light is turned on.
      selector:
        entity:
          domain: light
    secondary_light:
      name: Mirror light
      description: This is the secondary light, will be turned off when the primary light is turned off.
      selector:
        entity:
          domain: light

trigger:
  - platform: state
    entity_id: !input secondary_light
    to: "on"
  - platform: state
    entity_id: !input primary_light
    to: "off"

action:
  choose:
    - conditions:
        - condition: template
          value_template: "{{ trigger.to_state.state == 'on' }}"
      sequence:
        - service: light.turn_on
          entity_id: !input primary_light
    - conditions:
        - condition: template
          value_template: "{{ trigger.to_state.state == 'off' }}"
      sequence:
        - service: light.turn_off
          entity_id: !input secondary_light
  default: []