Select multiple entities to link their on/off state. If any selected entity is turned on or off, the other selected entities will be sent a matching on or off command.

link_multiple_devices.yaml

blueprint:
  name: Link On/Off State of Multiple Devices with Configurable Delay
  description: "## Link On/Off State of Multiple Devices v1.0.4

    Select multiple entities to link their on/off state. If any selected
    entity is turned on or off, the other selected entities will be sent
    a matching on or off command after a configurable delay.

    You can select any entity, but only entities supported by the
    `homeassistant.turn_on` or `homeassistant.turn_off` service calls
    will work.

    ### Requirements

    * All selected entities MUST support `homeassistant.turn_on` and
      `homeassistant.turn_off` or errors will be logged and the blueprint
      will not work.

    * Requires Home Assistant 2022.5.0 or newer.

    ### Credits

    * [@adchevrier](https://community.home-assistant.io/u/adchevrier) for the
      [initial blueprint](https://community.home-assistant.io/t/synchronize-the-on-off-state-of-2-entities/259010)

    * [@hebus](https://community.home-assistant.io/u/hebus) for
      [this fantastic template](https://community.home-assistant.io/t/synchronize-the-on-off-state-of-2-entities/259010/38)"
  domain: automation
  homeassistant:
    min_version: 2022.5.0
  input:
    linked_entities:
      name: Entities to link
      selector:
        entity:
          multiple: true
    delay:
      name: Delay before action (seconds)
      selector:
        number:
          min: 0.0
          max: 60.0
          unit_of_measurement: seconds
          mode: box
          default: 0.0

mode: restart
max_exceeded: silent

variables:
  linked_entities: !input "linked_entities"
  delay: !input "delay"

triggers:
  - trigger: state
    entity_id: !input "linked_entities"

condition:
  - condition: template
    value_template: >
      {{
        trigger.to_state.state != trigger.from_state.state
      }}
  - condition: template
    value_template: >
      {{
        (trigger.to_state.state == "on") or
        (trigger.to_state.state == "off")
      }}
  - condition: template
    value_template: >
      {{
        trigger.to_state.context.parent_id is none or (
          trigger.to_state.context.id != this.context.id and
          trigger.to_state.context.parent_id != this.context.id)
      }}

actions:
  - delay: "{{ delay }}"
  - action: homeassistant.turn_{{ trigger.to_state.state }}
    target:
      entity_id: >
        {{
          expand(linked_entities) |
            selectattr("entity_id", "!=", trigger.entity_id) |
            map(attribute="entity_id") |
            list
        }}

Added 2-second delay to deal with dimmers (MCOHome). Without it, the dimmers will be stuck in their state.