18.04 LTS - Fourth button on titlebar

Question

I have suffered this weird button for a few days. It is really annoying to use customized icon themes (default one is fine).

Does anyone know what this is? I want to remove it.

Answer 1

Result of

gsettings get org.gnome.desktop.wm.preferences button-layout

should be 'appmenu:minimize,maximize,close'

if not

gsettings set org.gnome.desktop.wm.preferences button-layout appmenu:minimize,maximize,close

Answer 2

I decided to get into dconf and see this configuration. Question solved.