room_lights_count.yaml

---
platform: template
sensors:
  ROOM_CODE_lights_count:
    friendly_name: "ROOM_NAME Lights Count"
    value_template: >-
      {% if not is_state('light.ROOM_CODE_lights', 'on') and not is_state('light.ROOM_CODE_lights', 'off') %}
        {% set value = "0" | int(0) %}
      {% else %}
        {% set value = states |
          selectattr('entity_id','in',state_attr('light.ROOM_CODE_lights','entity_id')) |
          selectattr('state','eq','on') | map(attribute='entity_id') | list | count | int(0)
        %}
      {% endif %}
      {{value | int(0)}}
    attribute_templates:
      total_lights: >-
        {% if not is_state('light.ROOM_CODE_lights', 'on') and not is_state('light.ROOM_CODE_lights', 'off') %}
          {% set value = "0" | int(0) %}
        {% else %}
          {% set value = states |
            selectattr('entity_id','in',state_attr('light.ROOM_CODE_lights','entity_id'))|
            selectattr('state','ne','unavailable') | map(attribute='entity_id') | list | count %}
        {% endif %}
        {{value|int(0)}}