Hello @Andbob

To add 'Category' to your Discussions App, please go to Studio -> Forms app -> Data Items -> Select Discussions module (from the dropdown field) -> Forum Categories -> 'Add New Item' button.

To add 'Categories', please go to Studio -> Forms app -> Categories -> Select Discussions module (from the dropdown field) -> 'Add' button.

To know the difference between 'Category' (singular) and 'Categories' (plural), please read this post:

https://una.io/cmts-view/1s20owo?sys=bx_forum&cmt_id=41055