If I understand what you mean, this is related to the way the Bootstrap Navbar (which is what this is using underneath) responds when completely collapsed. Basically the Navbar expands to fill the span of the Streamlit container, therefore even in mobile view, the Streamlit container doesn’t get small enough for the Bootstrap Navbar to switch to only using the icons for the menu. For example, as I shrink the window, the Streamlit container has a minimum width that holds the menu from getting any smaller. So it is responsive, it can only respond within the container Streamlit gives it though.
Start
Shrink
Smallest I can shrink it