@TWid19, @Paul Telkamp sums up the issue pretty well--Calendars, being a piece of the SharePoint site, are not made to be publicly accessible and making their content public requires some outside work.
As an alternative solution if you're using O365, you could look into leveraging a dummy E1 O365 account, a Flow, and your SharePoint calendar. The idea would be to have your dummy E1 O365 account publish its Outlook calendar publicly, and you'd depend on Flow to copy any event you've made in your SharePoint calendar into your dummy account's Outlook calendar. You might have a hard time updating events, but if your calendar items don't change much, you won't have a problem. This method directly costs your organization a bit of extra money with a stagnant E1 account, but it's one of the "simpler" solutions out there.
