actix-admin/templates/form_elements/checkbox.html

<input 
    class="{{ model_field | get_html_input_class }}" 
    type="{{ model_field | get_html_input_type }}"
    value="true" 
    name="{{ model_field.field_name }}" 
    placeholder="{{ model_field.field_name }}"
    aria-label="{{ model_field.field_name }}" 
    {% if model.values | get(key=model_field.field_name, default="false") == "true" %}checked{% endif %}
>