The new calendar in Microsoft Teams now generally available

This new feature is an absolute nightmare for the tenants that do not have the OWA enabled. When the users access their Teams, it pops up a message about the new Calendar and make users to enable it, and once user switches the toggle, it returns 400 Error message and there is no button to revert back to the origianl calendar on Teams. The only way to go back to the old calendar is to clear the cache both on Desktop teams and teams for web. 

No official documents nor the announcement in message center in m365 admin center says the OWA MUST be enabled for this feature to be used and there is no option to remove or disable new Calendar toggle in the app completely for all users.

What is even crazier is that, although the tenant doesn't have have OWA enabled, there are few users who were able to access the new calendar and it took me forever to figure that the users did enable OWA once before for test purposes. Therefore, all users in the tenant currently unable to access OWA, but only few users are able to use the new calendar and rest of the users are all experiencing the 400 error and it causes so much extra time and efforts to notify users to not switch to the new Calendar. It is indeed frustrating! For all users to be able to access the new calendar, I have to enble OWA for all uesrs and somehow ask them to access it at least, which doesn't make any sense.