I know it is missing, I’ve disabled it. Why do I have to keep on seeing the warning message?
Presumably because LO has a dependency on a related external library[1]. Incidentally, which LO packages did you install? Similar cases seem to point to a packaging-related cause i.e., not having all the requisite packages installed. Related thread here.
[1] A brief look at the source code would seem to indicate that Xserver + Xinerama are used in handling multiple screens forming one large display area i.e., virtual desktop.