How to fix duplicates in Outlook To-Do bar

This task list on the right is called Outlook To-Do Bar.

The add-in syncs tasks in the Projects folder, My Issues folder, My watched folder, and a folder that related to a project. So, can be duplicated in To-Do Bar.

As a workaround, you can set a filter to display only tasks from specific folders.

You can try to right-click on the header of the To-Do bar, select View Settings there, after that click the Filter button.

In the Filter dialog window go to the Advanced tab, click the Field button, select All Task Fields > In Folder in the menu. Choose Condition to 'is (exactly)'.

Type the required folder's name in the Value text box and click Add to List button below. We recommend typing the Projects folder. The name of a folder depends on your localization, please check it.
 
Click OK, then OK again. You'd now set up a filtered view for your tasks in the Outlook To-Do Bar.

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Check this video on how to customize your To-Do list with activities from the Task manager: How to customize Outlook To-Do Bar with activities from Ahau Software Integrations