Graph API explore, also does not show me all events either (ref: Graph Explorer - Microsoft Graph using “https://graph.microsoft.com/v1.0/me/events?$select=subject,start,end”). In the diagram below, one of the most recent events it shows me is (none after 2021-09-07 though):
Yet in my calendar, I have:
This lends me to believe this is an account / licensing / API issue.
(Of particular note could be the “Exchange Online (Plan 1)” with doesn’t specifically list Exchange as compared to Microsoft 365 Business Standard (ref: Compare Microsoft Exchange Online Plans).