Group calendars in 3rd party application

Hi,

I couldn't find a way to show events (created/accepted in a group calendar) in a third app application (calndar in MacOs, Calendar in Spark Mail app, ...). This is crucial, as moving back and forth from different devices and workplaces should be a seamless operation during these days. 

I can only see events in my "Calendar" from Outlook (where of course I see all the events, also those coming from groups).

Thanks