Hi @Jean Bisson ,
For SPO calendar, it's just a special list in SharePoint site. To get the events in SPO calendar, it's the same as getting listItem in a list.
To use MS Graph api to get listitem, you should use get listItem method. Please refer to this article for more: https://learn.microsoft.com/en-us/graph/api/resources/listitem?view=graph-rest-1.0
And you need to grant Sites.Read.All permission.
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