In settings > window manager there is no option for minimize anymore. It seems to have gone. I have tried restarting the wm etc; any ideas?
On the Style tab? Is it missing or greyed out? (If its greyed out, the window manager theme doesn't support it).
What version of Xfce are you running and what version of xfwm4?
Can you post a screenshot?
ii xfce4 18.104.22.168
This is xfwm4 version 4.8.3 (revision 360ccf2) for Xfce 4.8
And I did used to have the minimize button.
That's an interesting set of icons you have there. I think one of them is the minimize button. If you hover your mouse over them, does a pop-up hint display that identifies them? Try changing your icon theme to see if you get a different set of icons.
Yes hovering over them gives a hint but there is no minimize. The closest to that is "Hide".
Changing to the Tango icon them did not make a difference.
I still cannot find the minimize button for my windows.
Hide is the one I needed. I just tried it; so it is not called Minimize, rather - Hide.