123 Sync for Google Fit use and transfer to any other app of information received from Google APIs will adhere to Google API Services User Data Policy, including the Limited Use requirements.
Or in more simple words:
The Google Spreadsheet™ Editor add-on uses only the spreadsheet that the add-on is installed in.
Add-on will only read your heart rate, same for weight and your steps. Hence it needs read access to your heart rate data, body measurements, physical activity data.
For doing this it needs access to the external Google Fit service. Google Fit is the only external service in use.
Optionally you can create a periodic schedule to update your sheet.
As it is an Google Spreadsheet add-on it will display a sidebar in the spreadsheet and show relevant prompts.