Previously, this area had an interface with buttons and their functions listed. There used to be a button to hide the interface, but now it’s gone. I couldn’t find an option for this in the settings.
by default I think its
/
You can toggle it but leave the keybind used to toggle it visible, or you can press and hold the keybind to hide it entirely. So its not a setting.
Edit:
Controls > Common > “Collapse/expand action bar in battle”