How was this made with CiviCRM?

This is not really a use case but a showcase for the functionality of one extension in CiviCRM. It is therefore different from all other topics on this site.

The Outlook 365 integration extensions can be found here.

The Gitlab page contains the extensions as well as an instruction on how to set it up in both your CiviCRM environement as well as on your Outlook 365 clients.