Automation only turn power off if TV is off, else send notification

Configuration
3

The problem is here:

  - service_template: >
      {% if states('sensor.blitzwolf_01_wattage') | float < 40 %}
        switch.turn_off
      {% else %}
      {% endif %}
    entity_id: switch.blitzwolf_01_relay

You can’t set service_template to nothing, it must be a valid service. However, what you can do is specify a non-existent entity. Home Assistant won’t complain if you attempt to turn off a switch that doesn’t exist.

We can leverage that information to achieve what you want:

  - service: switch.turn_off
    data_template: 
      entity_id: "{{ 'switch.blitzwolf_01_relay' if states('sensor.blitzwolf_01_wattage') | float < 40 else 'switch.none' }}"

EDIT
Corrected the example; overlooked to include data_template: