Created attachment 8688 Grayed out un-clickable box. The search box is gray and disabled in the settings manager sub-items. This is quite misleading until we learn that, e.g. in the theme I'm using, the enabled one is white and the disabled one is gray. If there's no intention of enabling it in sub-items that can used it (like, currently MIME type editor and xfconf editor have their own search fields), then having no search box at all in the sub-items will prevent people wondering why it isn't working (I'm not so dumb, but I installed the system from a basic iso and wondered if I had some package missing before I realized that the box actually was disabled).
Note in the screenshot that the check boxes, which are active, are gray with my theme (Bluebird), so no wonder I thought the search box should be active too.
Created attachment 8695 screenshot Alternatively, the opacity of the search box could be lowered.
Definitely better to display that it isn't active.
Created attachment 8708 settings-manager-hide-search.diff I would hide the search entry altogether, the attached diff accomplishes this (whoever pushes this can take authorship).
I consider this a wontfix because your Gtk+ theme is responsible for making you aware that an item is insensitive/unusable. Modifying the opacity of a widget in the code on top of the theme is not just disrespecting the theme's design, it is also potentially irritating and even more confusing than what you describe. Hiding the widget feels very disruptive, even though in this case it'd be the preferable option. From my point of view the better solution is to leave things as they are. I don't see the problem with the insensitive widget. There are a lot of other conditional dialogs that make widgets/items sensitive/insensitive based on other settings.
(In reply to Simon Steinbeiss from comment #5) 100% Agreed.
Alright, closing as wontfix then.