I think it is a common practice to change the layout tabs below each other instead of side-by-side in small screens. That would make them accessible quite quickly.
...you could change categories and notifications to icons on mobile. The tabs might still fit that way.
Regarding no title posts: In a BB, I tend to usually ignore all posts without a title or with a click bait title. If people do not take the time to explain in a few words why I should read it, it's not worth my time. That maye different in timeline-based communication (although I prefer titles there, too). I think a common practice to identifiy a thread in an overview is to display first few words of a post - unless it has a summary - unless it has a title (DisplayTitle = post title; if not present = post summary; if not present = first X characters of post).
I mainly work with the notification tab, I would not get rid of it.