from the wppizza->access rights page :

Menu Items and Categories are accessible just like “normal” posts

i.e access to menu items and categories are managed by wordpress just like access to “normal” posts/categories

personally, i would probably use some role management plugin and create a new dedicated role you can assign access to as you need want .

Generally I also do not think giving editing capabilities to subscribers is a good idea really. but that’s up to you of course and will always depend on your circumstances