Add Uncategorized to the user’s sidebar categories editor and remove both the search bar and the dropdown button, they’re not really necessary for only 9 (including Uncategorized).
Could you please post a screenshot to make it more clear what you’re referring to?
It’s this 
, in the user’s menu, to edit the sidebar categories.
Uncategorized is missing and the only categories which I use in this forum are Uncategorized and Site Feedback. Then the search bar and the dropdown button aren’t necessary because the list is very short. By the way General or Generic would be better than Uncategorized.
We use a hosted forum software that only offers limited control, so I don’t think we can do anything here.
Yes, alright, I understand, you’re using Discourse as Zorin Forum in which I’m particularly active. This Uncategorized section is there, too, but it’s a kind of “ghost category”, it’s hidden in the domain links tree and I also showed it to the moderators there, they didn’t even know it existed 
. If you want to see it here’s the link 
Uncategorized - Zorin Forum. You can see that by entering the menu and clicking All Categories Uncategorized is missing but in the search bar in the categories filter Uncategorized is a choice.