Hi,
I’ll need some more info here.
The title says “new topic” button, but the OP says “new thread” button.
I’ve just enabled material design for myself, and on meta (with latest version of the theme), there are no floating buttons I can see.
Can you show a larger screenshot (full screen) and add what version of Discourse and the theme you are on, as well as what device and browser version?
Or share the link of the forum where you encounter this.
Cheers