I have solved with this sensor, thanks for your template.
in this sensor I set the number of events of the day as status and then the attributes.
- platform: rest
name: Evento 1
authentication: basic
headers: {'Authorization': "Bearer XXX"}
scan_interval: 60
resource_template: "https://homeassistant.local:8123/api/calendars/calendar.lavoro?start={{ now().strftime('%Y-%m-%d') }}T00:00:01Z&end={{ now().strftime('%Y-%m-%d') }}T23:59:59Z"
value_template: '{%- for bd in value_json -%}{%- if loop.last %}{{ loop.index }}{% endif -%}{%- endfor -%}'
json_attributes_path: "$[0]"
json_attributes:
- summary
- start