Can I share a calendar that isn't my main personal one on Sharepoint?

Claudia_Conway If you are using SharePoint team site connected with M365, you can use group calendar from outlook as well as you can add Group calendar on SharePoint site page using Group calendar web part 

Note: It does not have calendar like UI (month/week layout).

If you want a calendar just on SharePoint site and not required it inside outlook, you can use SharePoint list with modern calendar view. Check: Create a modern Calendar view in SharePoint Online/Microsoft Lists 

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