Apart from the really necessary UI button "Close plugin" in the plugin window bar, it would be great if you could show/hide all other UI buttons (each one separately) as you wish. Ideally, there should be a global setting that applies to all plugins. You can also override this for each individual plugin window

by changing the setting for each window of a plugin instance.

This can be particularly helpful on the iPhone, i.e. on very small displays.

If there is no more space, less important UI buttons can also be shown/hidden with a hamburger menu.