On iOS, Safari as well as Discourse Hub when you open the chat the top part gets overlapped by the header. So the minimize/close buttons aren’t visible, tapping on the logo is the only way out.
Just saw this topic, looks like Android, the same issue appears there:
Is there a theme (or theme component) that makes the chat go to the sidebar instead of floating above the Discourse topics?
Most displays today are wide enough to allow the topics and the chat side by side easily.
Chat is full screen when you do the above, not side by side with topics. But that can be addressed by opening a separate window and putting them side by side.