Filter your task list by category
You can assign an Outlook task to one or more categories. Open the Outlook task, and click on the down-arrow under Categorize in the ribbon tab. This will allow you to select a category for the task. You can customize the name of a category by clicking on Rename.
The assigned category will appear in the Categories column of your task list in the app:
You can filter your task list by category by clicking on the filter icon in the column header:
This will give you a drop-down list from which you can select the filter:
The filtered list will include some tasks that are not specifically assigned to a category. This is because, in addition to the categorized tasks, the filtered list shows the children of the categorized tasks, as well as its ancestors to the root task.
You can also filter your tasks by category by selecting a category from the drop-down list in the Tasklist ribbon tab: