I'm having the same issue regarding Calendar not working on 12.7.2.
I just did a clean install of macOS 12.7.2 on a MacBook Air 11" 2015. When configuring iCloud, for which I rely solely on sync'ing Contacts and Calendar, while Contacts populated and worked correctly, Calendar had the following probems: (1) no events showed; (2) all my iCloud calendars were shown in the left pane were duplicated (and all were checked on, but no events from any of them showed). I also have other Macs running 12.7.1, and Calendar is working normally. The version of Calendar on both 12.7.1 and 12.7.2 is Version 11.0 (2855.6.1). So, this seems to be an issue clearly with the 12.7.2 macOS upgrade rather than Calendar itself. I have paused the installation and thus have not tried Mail. Hoping others will chime in if they see similar problems and that this catches the attention of Apple.