https://answers.microsoft.com/en-us/windows/forum/all/windows-11-doesnt-show-my-calendar-on-taskbar/7995182e-e59e-492e-b6d1-36393f980292?page=2

1. Win + R   --> regedit 

2. add a new DWORD value or modify it. 

HKEY_CURRENT_USER\Software\Policies\Microsoft\Windows\Explorer\DisableNotificationCenter   0

HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\PushNotifications\ToastEnabled    1

3. Reboot