I managed to work it out
mqtt:
- sensor:
name: Dahua Car Score
state_topic: "frigate/events"
unit_of_measurement: "%"
value_template: |-
{% if value_json['after']['label'] == 'car' and value_json['after']['camera'] == 'dahua' %}
{{ (value_json['after']['score'] | float * 100) | round (1) }}
{% else %}
{{ '0' }}
{% endif %}