Windows 11 does not include a standalone, OS-native Calendar app that is completely unassociated with email applications. The primary calendar functionality is integrated into the Outlook app, which is part of the Microsoft 365 suite. If you do not wish to use Outlook or third-party applications, you may find that your options for a calendar app are limited within the Windows 11 environment.
For users looking for calendar features, the Microsoft 365 companion apps, which include a Calendar companion, are designed to enhance productivity by providing quick access to calendar events directly from the Windows taskbar. However, these apps are still tied to Microsoft services.
If you require a calendar app that is not linked to your email or Outlook, you may need to explore third-party options, as the native offerings are primarily integrated with Outlook and Microsoft 365 services.