1. Right-click Start then select Run.
  2. In the Open box, type:
  3. Outlook.exe /resetnavpane


  4.  Then click OK.


source: https://support.microsoft.com/en-us/office/i-can-t-start-microsoft-outlook-or-receive-the-error-cannot-start-microsoft-office-outlook-cannot-open-the-outlook-window-d1f69da6-b333-4650-97bf-4d77bd7abb85