You can allow moderators to create categories, but not regular users.
I’m curious… why would you want users to create categories? They are so important to the organization and presentation of your community that it could get pretty weird, pretty fast. Generally you want to keep the number of categories to a minimum anyway.
You can enable users to create tags if you like. It defaults to trust level 3 but you can lower that to trust level 0 if you want to.
How wondering how are you allowing your moderators to create categories? We’re on discourse 2.1.6, and when we make an end-user (no admin rights) a moderator, we still don’t see the drop down button to create categories.
Did you do any customizations? Or used any plug-ins?