Does NixOS support the MATE desktop environment? I see that there are some MATE packages, e.g. mate.caja, mate.pluma. But MATE is not in the manual’s list of desktop managers (chapter 9):
Thus you should pick one or more of the following lines:
services.xserver.desktopManager.plasma5.enable = true;
services.xserver.desktopManager.xfce.enable = true;
services.xserver.desktopManager.gnome3.enable = true;
services.xserver.windowManager.xmonad.enable = true;
services.xserver.windowManager.twm.enable = true;
services.xserver.windowManager.icewm.enable = true;
services.xserver.windowManager.i3.enable = true;