titlebar actions (lower, menu, minimize, none, toggle maximize, toggle maximize horizontally, toggle maximize vertically, toggle shade)

• double-click
• middle-click
• secondary-click

titlebar buttons

• maximize (show/hide)
• minimize (show/hide)
• placement (left/right)

see also

• https://docs.gtk.org/gtk3/class.Settings.html
• The Softwares Windows Titlebar Decorations doesn't properly allign with system settings app-center#792