When tested, this is the expected behavior, and events created by the Graph API are primarily integrated with calendars in outlook, so some created events can be seen in outlook calendars rather than displayed in teams.
This is true for group events created through the Graph API, which you can view in outlook's calendar.
For a more detailed explanation, you can check out the official document:
https://learn.microsoft.com/en-us/graph/outlook-calendar-concept-overview
Hope this helps.
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