Unless I’m missing something, there isn’t way to create a new unlinked topic when viewing a topic. To do so, you’d have to click the logo to go home (1 click) or the hamburger menu and then make a selection (2 clicks), both if which may not be entirely obvious to new users (at least before DC become the web standard!)
I think it should always be in the top right menu (what do you call that?) for logged-in users:
If that is not acceptable for some reason, I suggest making it an admin selectable option on the Admin>settings>basic setup, akin to the options available there for top menu.