Additional calendar-related features and issues within Microsoft Teams for Education
My screenshots are from new Teams desktop app... so it can work.
Try clearing the cache and repairing Teams apps.
Follow the instructions in this article to clear Teams cache. https://learn.microsoft.com/microsoftteams/troubleshoot/teams-administration/clear-teams-cache?WT.mc_id=M365-MVP-6934
Try repairing or resetting the app. In Windows Settings > Apps > Installed apps, find Teams then click on the dots on the right and choose Advanced Options. Repair is near the bottom of the page. .