ACP -> Extend -> Widgets:
Apply widget to "Categories" tab only, not "Global" or any of the others.
Screenshot_2020-07-02 Extend Widgets NodeBB Admin Control Panel.png
Does NodeBB offer hierarchical permissions that are inherited by subcategories?
My goal.. create multiple 'boards' as top-level categories, but only have certain people/groups have visibility to the top-level categories, but then I expect them all to be able to see the subcategories if granted access to the top-level categories. I also might want to have subgroups at levels of the tree that only see that subcategory and its children.
There are not hierarchical permissions in NodeBB. If you would like to see hierarchical permissions, you could open an issue on our Github page and request such a feature.
I do believe we have a way of copying permissions between groups, so that could help you out in doing what you want.