When changing the value for DecorationLayout in Settings Editor it has no effect on the order of buttons in the title bar - although this value is what is changed when amending the order of buttons in the window manager settings e.g. Open Settings Editor -> navigate to xsettings -> edit DecorationLayout order - has no effect on tittle buttons Open Settings Manager -> open window manager -> change order of buttons in button layout - changes order of title buttons and value of DecorationLayout in editor
There are two types of window decorations (which is confusing for users, I agree). One is the decorations drawn by the Gtk toolkit (handled by the xsetting you mention) and the other is drawn by the window manager (which is the second setting you mention). So just changing the xsetting will only affect applications that use so-called "client side decorations". The correct way to change the setting is not to go to xfconf directly but to change the layout through the window manager settings