Hi Wan,
I'm Ahmed and I am here & happy to help.
I apologize for the issue you are experiencing. Please be assured that I will do my best to provide a satisfactory response and assist you with resolving the problem.
Please check the following steps:
- Please check the behavior with Teams Web App:
https://teams.microsoft.com
- Please also make sure that the Exchange Online license is verified from the Admin Center > Users > Choose the affected user > Licenses and Apps
This issue could be caused by an app setup policy that does not include the calendar app. To fix this, you need to have admin access for your team and follow these steps:
- Sign in to Microsoft Teams Admin Center as a Microsoft Office 365 administrator.
On the left corner of the home screen, click Users, and choose your account.
Select the Policy tab for your account.
- Go to Global (Org-wide Default) under the App setup policy section to show the list of apps.
- Click the Add Apps button and select the Calendar app.
- Restart your MS Teams desktop client to see the Calendar tab.
For the steps details please check:
https://learn.microsoft.com/en-us/answers/quest...
I hope this helps! Let me know if you have any further questions or concerns.
Best regards,