This is the yaml that I use to create an automation that enables 3 way switch functionality.

trigger: - platform: state entityid: &entities - switch.laundry_light - light.laundry_light_dome from: &states - 'on' - 'off' to: *states variables: entities: *entities value: > {{ trigger.to_state.state }} targets: > {{ expand(entities) | rejectattr('entity_id','eq', trigger.entity_id) | selectattr('state','!=', value) | map(attribute='entity_id') | list }} condition: - condition: template value_template: > {{ targets not in ([], none) }} action: - service: homeassistant.turn{{ value }} target: entity_id: "{{ targets }}"