1. Make sure Microsoft Teams and Microsoft Calendar are both under your primary Outlook account or email address.
2. Check in the Microsoft Calendar app that the calendar you want to view is selected and visible within the app.
3. Check in the Teams app that your necessary settings and integrations are properly configured in the app.
4. Ensure the account you're using inside Teams is the same as the account you use to access your Microsoft Calendar.
5. Try restarting your device, or reopening the Microsoft Teams and the Microsoft Calendar apps.