I verified that the hamburger button in the composer isn’t labeled. Specifically, this is the toggle-toolbar button in the composer-toggles component. This button is only rendered in the mobile view.
What would be a reasonable label for this button? Maybe “Formatting”, since many of the toolbar options are formatting related? Not all of them are, though. Maybe the more generic “Tools” would be better.
It occurred to me that, to enable accessibility fixes to reach Discourse’s worldwide user base without imposing too much on translators, we should use existing strings for unlabeled controls when it makes sense. So, for the hamburger button, would it make sense to use “show more” as the title? We could use “options”, and I think that would be a better fit, except that there’s already an “options” button in the toolbar itself. I think that would be confusing.