@PitaJ is correct, the option is called the "tags whitelist", and you can decide which tags to allow, and do so on a per-category basis
how is the "unresolved" working? seems like not a tag, but what is it?
I noticed in this category there is a topic (topic title: " MongoDB Structure") which has a tag (but not like a tag) called "unresolved". is it really a tag or something else? how to add something like this to a topic?
Its a plugin I made: https://github.com/psychobunny/nodebb-plugin-question-and-answer