@Naddzie ,
User could hide calendar in teams client as below. Right click the Calendar app in the left bar and choose unpin. Then, it will be hidden.
For more information, please refer to the following two articles:
https://support.microsoft.com/en-us/office/pin-an-app-for-easy-access-3045fd44-6604-4ba7-8ecc-1c0d525e89ec
https://learn.microsoft.com/en-us/microsoftteams/teams-app-setup-policies
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