Menubar is not hidden automatically, as it is done in Firefox. For example, when you click the left mouse button (actually, you can press almost any button) outside the menu area, the menubar is hidden, but here it remains visible, you can hide it only by clicking the alt button again. And when activating any submenu, the menubar should also be hidden. Otherwise there is little point in this setting, the menubar remains visible.

Firefox

Keepassxc