Go to Settings  and then Project Sets

Create a Set by pressing the plus button next to the dropdown menu.

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Give your Project Set a title, select an icon that is relevant to the theme of your Set from the dropdown menu, and then choose a colour from the colour selector. Hit "Add and Close" when you are done.

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Adding Items to Project Sets

Now you have set up your Project Set, it's time to add your items.

Go to the item e.g. Card, Board, List, Kanban, Rundown, or Day Schedule, and then hit the dropdown arrow in the toolbar at the top right and "Add to Project Set" from this menu.

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Select the Project Set(s) from the dropdown menu "Choose Project Set" and then hit "Save" to add.